Specialized diets, "Leopard Frogs", and re-thinking assumptions...

I'm fascinated by the dietary preferences of fishes. How they've evolved over eons to consume various items found in their environments; how many fishes became "specialists" as an adaptation to the habitats in which they live.

And, as an aquarist who derives great pleasure from seeing his fishes "live off the land" and consume foods from the aquarium environment in which they reside, I really find some of the seunderlying feeding strategies fascinating. One of the more interesting examples is the consumption of wood by various species of fishes.

We read a lot about fishes which eat wood and wood-like materials.

Of course, the ones that come immediately to mind are the Loricariidae, specifically, Panaque species. Now, I admittedly am the last guy who should be authoritatively discussing the care of catfishes, having maintained maybe a couple dozen or so species during a lifetime of aquarium keeping. However, I do understand a little bit about their diets and the idea of utilizing wood- and botanical materials- in the aquarium for the purpose of supplementing our fishes' diets!

And of course, I'm equally fascinated by the world of biofilms, decomposition, microorganism growth and detritus...And this stuff plays right into that! 

Now, the idea of xylophagy (the consumption and digestion of wood) is of course, a pretty cool and interesting adaptation to the environment from which these fishes come from. And as you'd suspect, the way that wood is consumed and digested by these fishes is equally cool and fascinating! 

It's thought by ichthyologists that the scraping teeth and highly angled jaws of the Loricariidae are a perfect adaptation to this feeding habit of "scraping" wood. And of course, it's even argued among scientists that these fishes may or may not actually digest the wood they consume! While scientists have identified a symbiotic bacteria which is found in the gut of these fishes that helps break down wood components, it's been argued by some the the fishes don't actually digest and metabolize the wood; indeed deriving very little energy from the wood they consume!


In fact, a lab study by Donovan P. German was described in the November, 2009 Journal of Comparative Physiology, in which several species were fed wood and found to actually digest it quite poorly

"...in laboratory feeding trials, (Pterygoplichthys cf. nigrolineatus and Hypostomus pyrineusi)  lost weight when consuming wood, and passed stained wood through their digestive tracts in less than 4 hours. Furthermore, no selective retention of small particles was observed in either species in any region of the gut. Collectively, these results corroborate digestive enzyme activity profiles and gastrointestinal fermentation levels in the fishes’ GI tracts, suggesting that the wood-eating catfishes are not true xylivores such as beavers and termites, but rather, are detritivores like so many other fishes from the family Loricariidae."

Did you see that? Detritioves. Like, they're taking in wood to get other stuff out of the deal... And detritus is comprised of stuff like macrophytes, algae, and particulate organic carbon.


And this little nugget from the same study:  "...The fishes consumed 2–5% of their body mass (on a wet weight basis) in wood per day, but were not thriving on it, as Pt. nigrolineatus lost 1.8 ± 0.15% of their body mass over the course of the experiment, and Pt. disjunctivus lost 8.4 ± 0.81% of their body mass.

Oh, that's weird.

Yet, anatomical studies of these fishes showed that the so-called "wood-eating catfishes" had what physiologists refer to as "body size-corrected intestinal lengths" that were 35% shorter than the detritivore species. What does this mean? Could they have perhaps had at one time- and subsequently lost- their ability to digest wood?



And to make it even weirder, check out this passage from a study by Lujan, Winemiller, and Armbruster:

"Loricariids have a dense endoskeleton and are covered with dermal plates composed primarily of calcium phosphate, giving them a high physiological demand for dietary phosphorus. Paradoxically, the rivers and streams inhabited by loricariids as well as the detritus and biofilm that most loricariids consume tend to be highly Phosporus deficient."

The same study noted that, "Loricariids as a whole are largely unable to digest lignocellulose, and instead derive most nutrients and energy from easily digestible breakdown products (e.g., disaccharides and dipeptides) that are produced during microbial degradation of submerged, decomposing wood."

Oh, interesting!

I think it's yet another case of us as hobbyists drawing innocent conclusions based on anecdotal or superficial observations. I mean,"... they're munching on my wood, therefore, they must be 'eating' it!"


Now, to the point of the argument that most loricariids are primarily detritivores, consuming a matrix of biofilm, algal growth, microorganisms, and (for want of a better word) "dirt"- what does this mean to us as hobbyists? Well, for one thing, this has made them remarkably adaptable fishes in the aquarium. They will definitely rasp at wood", but according to the studies I just cited, they are not "eating" it, per se.

Now, my personal experience with Loricariidae is nothing like many of yours, and an observation I've made over the years is at best anecdotal- but interesting:

If you follow "The Tint", you know I've had a years-long love affair with Peckolotia compta aka "L134 Leopard Frog"- a beautiful little fish that is filled with charms. Well, I recall, are years back, that my first specimen seemed to have vanished into the ether following a re-configuration/rescape of my home blackwater/botanical-method aquarium. I thought somehow I either lost the fish during the re-scape, or it died and subsequently decayed without my detecting it... Pretty upsetting either way, but I couldn't find any trace of it!

For almost three months, the fish was M.I.A., just....gone.

And then one, day- there she was, poking out from the "Spider Wood" thicket that formed the basis of my newer hardscape! To say I was overjoyed was a bit of an understatement, of course! And after her re-appearance, she was out every day. She looked just as fat and happy as when I last saw her in the other 'scape...which begs the question (besides my curiosity about how she evaded detection)- What the fuck was she feeding on during this time?

Well, I suppose it's possible that some bits of frozen food (I fed frozen almost exclusively at that time) got away from my population of hungry characins and fell to the bottom...However, I'm pretty fastidious- and the other fishes (characins) were voracious mid-water-column feeders! To think that any appreciable amount got away from the hungry hoard was a bit hopeful. I believed at the time (and now am fully convinced) that it was more likely the biofilms, fungal growth, and perhaps some of the compounds from surface tissues of the "Spider Wood" I used in the hardscape that she was feeding on.

"Spiderwood" (aka Azalea root) stuff does recruit significant biological growth on it's surfaces when submerged , and curiously, in this tank, I noticed that, during the first few months, the wood seemed to never accumulate as much of this stuff as I had seen it do in past tanks which incorporated it!

I attributed this to perhaps some feeding by a population of Nanostomus eques, which have shown repeatedly in the past to feed on the biofilm or "aufwuchs" accumulating on the wood.

I'm sure that was a valid observation, but they were actively taking prepared foods as the bulk of their diet, so I have a hard time that they solely were responsible. 

There was also a layer of Live Oak leaves distributed throughout the booth of the wood matrix, which, although they break down very slowly compared to other leaves we use, DO ultimately soften over time and break down over time. Since they are rather "durable", they do accumulate a lot of fungal growth and biofilms on their surfaces.

Interestingly, in this tank, I was finding little tiny amounts of very broken-down leaves, which I attributed to decomposition, but thinking back on it, looks more like the end product of "digestion" by someone!

I don't think I ever saw my L134 consuming prepared food. When I did observe her activities, she was seemingly "grazing" away at the wood surfaces and on botanicals...That's all the proof that I needed to confirm my theory that she's pretty much 100% detritivorous, and that the botanical-method aquariums she's resided in provide a sufficient amount of this material for her to consume.

To this day, I've never seen her eat prepared foods!

I have since acquired three captive-bred specimens from my friend, master breeder Sumer Tiwari, and this group has been seen to take prepared food on occasion. At the very least, adding some pellets or frozen foods seems to initial some kind of response in the fish, wether they appear to eat it or not.

So, back the the whole "xylophore thing"... After reading the studies I mentioned, I think that in the aquarium, as well as in the wild, much of what we think is actually "consumption" of the wood by the fishes is simply incidental- as in, the fishes are trying to eat the biocover and detritus on the surface tissues of the wood, and perhaps obtain some nutrition from the compounds contained in the softer portions of the wood. They apparently do a pretty good job (with their specialized mouthparts) of rasping away the surface tissues of the wood!

So, yeah- apparently, some of the wood may pass through the digestive tract of the catfishes, but it's passed without metabolizing much from it...perhaps like the way chickens  consume gravel, or whatever (don't they? City boy here! WTF do I know about chickens!)...or the way some marine Centropyge angelfishes "nibble" on corals in their pursuit of algae, detritus, and biofilms.

Again, my perusal of German's scientific paper seems to support this theory:

"Catfishes supplement their wood diet with protein-rich detritus, or even some animal material to meet their nitrogen requirements. Although I did not observe animal material in the wood-eating catfish guts, Pt. disjunctivus did consume some animal material (including insects parts, molluscs, and worms), and all three species consumed detritus."

And finally, the "clincher", IMHO: "The low wood fiber assimilation efficiencies in the catfishes are highly indicative that they cannot subsist on a wood only diet."



I mean, it's just one paper, but when he's talking about isotopic tracing of materials not consistent with digestion of wood in the guts of Loricariids, I think that pretty much puts the "eats wood" thing to bed, right? His further mention that, although some cellulose and lignin (a component of wood and our beloved botanicals!) was detected in the fish's fecal material, it was likely an artifact of the analysis method as opposed to proof that the fishes derived significant nutrition from it.

So what does all of this stuff mean to us? 

Well, for one thing, once again- detritus/biofilm/fungal growths = good. Don't loathe them. Love them.

Your fishes apparently do.

I think it means that, as hobbyists probably knew, theorized, and discussed for a long time- that the Loricariids consume detritus, biofilms, and prepared foods when available. This is not exactly earth-shattering or new.

However, I think understanding that our botanical-method aquariums can- and do- provide a large amount of materials from which which these and other fishes can derive significant nutrition furthers my assertion that this type of system is perfect for rearing and maintain a lot of specialized feeders. 

Materials like the harder-"shelled" botanicals (ie; "Skyfruit" pods, Cariniana pods, Mokha pods, bark, etc.) tend to recruit significant fungal growths and biofilms, and accumulate detritus in and on their surfaces. And of course, as they soften, some fishes apparently rasp and "consume" some of them directly, likely passing most of it though their digestive systems as outlined in the cited study, extracting whatever nutrition is available to them as a result. This is likely the case with leaves and softer botanicals as well.

Incidental consumption.

The softer materials might also be directly consumed by many fishes, although the nutrition may or may not be significant. However, the detritus, fungal, and microorganism growth as a result of their decomposition is a significant source of nutrition for many fishes and shrimps.

Detritivores (of which the amount of species in the trade is legion), have always done very well in botanical-method aquariums, and the accumulation of biofilms and microbial growth is something that we've discussed for a long time. By their very nature, the structure and decomposition of botanical materials make the "functional aesthetics" of our aquariums an important way to accommodate the natural feeding behaviors of our fishes.

So, the answer to the question (literally!), "Who has the (literal) guts for this stuff?" is quite possibly, "everyone!" 

Now, while while we're on the subject of loricariids, a further scan of scientific literature revealed some interesting things about what these fishes are actually taking in when they "graze" in the wild. It's kind of eye opening, to me. One study revealed that loricariids consumed five principal items: sponges, organic detritus, bryophytes, bryozoans and sediment.

Wood is definitely part of the equation somewhere, but for the species examined in one of the studies I found (Rhinelepis aspera, Hypostomus regani, H. ternetzi, H. maragaritifer, H. microstomus, and Megalancistrus aculeatus) the gut content analysis was quite revealing:

The food spectrum of R. aspera is primarily "organic detritus and small quantities of sediment"; with few periphytic organisms. Although H. regani was found to consume large quantities of organic detritus as well, it also consumed "plant detritus, various sediment, and periphytic organisms" (i.e.; bryozoans, sponges and aquatic insect larvae). Bryozoans and sponges, huh?

Wow! Freshwater sponges...

The study indicated that bryozoans and organic detritus were the main food food of H. ternetzi, which, according to the gut contents of a number of individuals,  tended to consume more sediment, rotifers, chironomids (i.e.; "Bloodworms'), gastropods and harpacticoids than the other species.

Harpactoids...you mean, like "copepods?" Stuff we as reefers feed all the time? H. margaritifer was found to ingest plant material. Other periphytic organisms such as insect larvae, and those bryozoans and sponges contributed to the diet of H. margaritifer.

And it gets more interesting still...

Sponges- I can't let that go.

Sponges were the principal food resource of H. microstomus and M. aculeatus, along with a healthy does of chironomids, various gastropods, Trichoptera (insects), and some bryozoans also consumed. Diets of these two fishes were composed of larger-sized items, with the finer organic detritus and such being less important than it was to the other species in the study. 

This kind of information is tantalizing. It's compelling. 

And what really gets me going is learning that some of our favorite, most beloved fishes are consuming large quantities of materials that I doubt any freshwater aquarist adds to his/her arsenal of foodstuffs. We're really good at feeding our catfishes baby vegetables and stuff, while typically overlooking many species' surprisingly high dietary dependency on items like insects, bryozoans, harpactoid copepods, and interestingly...sponges!

While we kind of always knew that these fishes ingested wood and "stuff", it's interesting to see what they're actually eating in the wild...especially the "stuff"- and configuring our aquariums and the supplemental and primary feeding opportunities available to the fishes accordingly.

We have some interesting, yet perhaps overlooked possibilities to provide some of these items. 

In fact, there are a number of marine aquarium-purposed foods (typically targeted at certain marine angelfishes, many of which consume significant quantities of sponge) which contain sponges in their formulation. One of my favorite is Ocean Nutrition's "Angel Formula." Granted, these foods contain stuff like mussels, and other marine foods, and the sponges included are marine sponges, but I can't help but wonder if these are that morphologically or nutritionally different/palatable to the fishes than a freshwater/tree sponge would be?

Could the next great frozen Loricarid food include sponges? And we DO have harpactoid copepods available live, and in a variety of other formats intended for marine fishes and corals...Interestingly, I remember that the big "knock" by us reefers, for a long time, about some of these copepods was that they were "freshwater" varieties, and therefore didn't have the "correct" nutritional profile for marine organisms.

Hmm. We're talking about freshwater fishes here, right? Yeah. 

So, like, why the hell haven't we been feeding these foods to our freshwater fishes all of these years?

Try some of these foods with your loricariids..and other fishes as well. What's to lose?

Oh, I can hear the objections: 


Is it?. Online ordering is really cool. It might just catch on.

"Too much work!" 

Really? C'mon. Ever cultured Grindal Worms or wingless fruit flies?  THAT is "too much work" by definition.

"This is ridiculous; No need to experiment with these wacky foods. We're doing just fine now with Zucchini and stuff! Stupid."  

Urghhhhh. "If man was meant to fly, he'd have wings..."

To not experiment is stupid, IMHO. 

Don't be stupid. And I mean that in the kindest way possible. Don't just accept "what works" as "the way." 

Push forward. Experiment. Fail quickly, or move forward rapidly with success. Play a hunch or two. Try something different. This is how advances in the hobby are made. This is how breakthroughs happen.

You gotta try.

Stay studious. Stay curious. Stay observant. Stay engaged. Stay resourceful...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Throwing some light on blackwater...

It goes without saying that the single most important component of our aquariums is also the most obvious...water! As the literal bearer of life and the environment in which our fishes, plants, and other organisms thrive, it's fundamental. it's the reason we're drawn to fishes, not gerbils, Tarantula, or Mice- or whatever other pets people keep!

Yeah, we're into water!

And I dear say that we take it for granted a bit.

Now, sure, some hobbyist rightfully place the importance of good quality, properly-conditioned water at the very top of their "want list" of "Stuff" required for successful aquariums. These are often fish breeders and very serious hobbyists, who understand the fundamental importance of good water for their work.

Some of the most common questions we receive lately are "How much _______ do I need to get my water to look like________?" or "How much_______ is needed to lower the pH in my tank?" Or, "How much do I need to get a good amount of humic substances and tannins into my aquarium?"

I usually respond with a simple, "I don't know."

These are all really good questions. Logical. Important.  I kind of feel like many hobbyists are looking for a plug-and-play "formula" or "recipe" for how to accomplish certain water-conditioning tasks.

I totally get that. But the reality is...there IS no "recipe" for how to do this stuff.

And it sucks, I know.

"Why, Scott? I read that you can just add some of this blackwater extract that you can buy online, and maybe add some catappa leaves, and..."

Stop. STOP. Please, we're just making this painful.

Simply adding leaves or bottled extracts to your tap water isn't going to result in "Instant Amazon" or whatever. There are numerous complexities and nuances which contribute to these habitats that to simply recommend adding "X" to your water isn't the whole story.

There are so many variables in the equation that it's almost impossible to give a definitive answer. And yeah, us guys in the botanical biz haven't really helped the situation. Over the years, vendors who sold catappa leaves, for example, would recommend starting amounts ("three leaves per 15 liters of water" or whatever...) of botanical materials to use in aquariums.

I mean, we've sort of done it, too...And, although our recommended "dosage" of leaves was given for different reasons (to avoid adding too much material to your tank too quickly), the idea of a "recipe" in general is kind of delusional, IMHO.

Now, this was all well and good, but it's based on....what? I mean, is this based on how many leaves of _______ size that a typical hobbyist with a 10-gallon aquarium needs to get the water "looking brown?" Or to lower tap water with a starting pH of 7.4 and a KH of ___ to pH of 6.9? Or to impart "x" ppm of tannins or humic substances into this given quantity of water?

See? Add to this story the fact that you really can't soften water and make it more "malleable" by using botanicals or extracts alone, and you've got a good case for confusion! It's just not that simple.

Maybe we can gain a bit of understanding- or at least, an appreciation for the dynamics of this process, by looking once again to Nature.

Have you very thought about how water reaches all of the wild aquatic systems of the world? I mean, it's got to get there some way, right? So, how does it reach the ponds, lakes, streams, and rivers and forest floors of the world?

Well, some simply falls into the body of water directly from the sky, and that's that. Some is a result of other overflowing streams and rivers (like, ya' know- those flooded Igapo forests we talk about!). Inputs of precipitation falling over the area of an aquatic habitat are transferred to the habitat via a number of different pathways.

It's surprisingly complicated.

There's like a whole field of science devoted to studying this process! It's called Hydrology, and it's incredibly interesting...As fish geeks, we're probably already acquainted with this field of study, at least tangentially! 

So, water comes from a variety of sources, reaching a myriad of ecological niches. However, not all of the water has such an easy journey on its way into our favorite aquatic habitat!

Even in the case of rainwater, some of it simply lands on tree leaves in the surrounding area and evaporates. This is a process scientists call "interception", and accounts for the fact that not all water makes it to the ground. Water that does reach the ground enters the soil through a process called infiltration. slowly percolating down to soil areas known as the "saturated zone"- and as you'd imagine, this is where the fun really begins! (to a soil geologist, at least!)

The soil properties control the infiltration capacity; these include things like soil permeability, the presence of vegetation and plant roots, and how much water is already in the soil. Through what is known as "ground water flow", ultimately, the water finds it way into our favorite aquatic habitats. It's important to note that soil texture ( the relative proportion of sand, silt and clay particles within the mix) affects infiltration rates. 

Sandy soils like the "podzols", common to forested areas of South America that we've talked about have higher permeability than some clay-based soils. In some really arid areas a "crust" can form on the soil surface, decreasing the permeability. And of course, the thickness of the soil directly affects how much water the soil can actually absorb.

And, in many cases, the substrate composition and its relationship with water has direct impact on the life forms which inhabit these aquatic systems. In the case of some habitats, like vernal pools, which are filled with water seasonally, the substrate is of critical importance to the aquatic life forms which reside there.

Yeah, soils and geology are perhaps the primary driver of water composition in Nature. 

Let's talk more about "blackwater."

In a blackwater environment, the color is a visual indicator of an influx of dissolved materials that contribute to the "richness" of the environment. Indeed, a blackwater environment is typically described as an aquatic system in which vegetation decays, creating  tannins that leach into the water, making a transparent, acidic water that is darkly stained, resembling tea.

But, that's not the whole story, really.

It’s important to really try to understand the most simple of questions- like, what exactly is “blackwater”, anyways?

A scientist or ecologist will tell you that blackwater is created by draining from older rocks and soils (in Amazonia, look up the “Guyana Shield”), which result in dissolved fulvic and humic substances, present small amounts of suspended sediment, and characterized by lower pH (4.0 to 6.0) and dissolved elements, yet higher SiOcontents. Magnesium, Sodium, Potassium, and Calcium concentrations are typically very low in blackwater. Electrical conductivity (ORP) is also lower than in so-called "whitewater" habitats.

Tannins are also imparted into the water by leaves and other botanical materials which accumulate in these habitats.


The action of water upon fallen leaves and other botanical-derived materials leaches various compounds out of them, creating the deep tint that many of us are so familiar with. Indeed, this "leaching" process is analogous to boiling leaves for tea. The leached compounds are both organic and inorganic, and include things like tannin, carbohydrates, organic acids, pectic compounds, minerals, growth hormones, alkaloids, and phenolic compounds.

Most of the of the extractable substances in the surface litter layer are humic acids, typically coming from decaying plant material. Scientists have concluded that greater input of plant litter leads to greater input of humic substances into ground water.

In other words, those leaves that accumulate on the substrate are putting out significant amounts of humic acids, as we've talked about previously! And although humic substances, like fulvic acid, are found in both blackwater and clear water habitats, the organic detritus (you know, from leaves and such) in blackwater contains more extractable fulvic acid than in clearwater  habitats, as one might suspect!

The Rio Negro, for example, contains mostly humic acids, indicating that suspended sediment selectively adsorbs humic acids from black water.  The low concentration of suspended sediments in rivers like the Rio Negro is one of the main reasons why high concentrations of humic acids are maintained. With little to no suspended sediment, there is no "adsorbent surface" (other than the substrate of the river, upon which these acids can be taken hold of (adsorb).

When you think about it, all of this this kind of contributes to why blackwater has the color that it does, too. Blackwater in the Amazon basin is colored reddish-brown. Why? Well, it has  those organic compounds dissolved in it, of course. And most light absorbtion is in the blue region of the spectrum, and the water is almost transparent to red light, which explains the red coloration of the water!

And many of those organic compounds come from the surrounding land, as touched on above...

In summary, natural "blackwaters" typically arise from highly leached (tropical) environments where most of the soluble elements in the surrounding rocks and soils are rapidly removed by heavy rainfall. Materials such as soils are the primary influence on the composition of blackwater.

Leaves and other materials contribute to the process and appearance in Nature, but are NOT the primary “drivers” of its creation and composition.


So, right from the start, it’s evident that natural blackwater is “all about the soils…” Yeah, I'll repeat it again: It’s more a product of geology than just about anything else. 

More confusing, recent studies have found that most of the acidity in black waters can be attributed to dissolved organic substances, and not to dissolved carbonic acid. In other words, organic acids from compounds found in soil and decomposing plant material, as opposed to inorganic sources. Blackwaters are almost always characterized by high percentages of organic acids.

Despite the appearance, as a general rule, blackwater rivers are lower in nutrients than clear rivers. Wouldn't it be interesting, when contemplating more natural biotope/biotype aquariums, to study and take into consideration the surrounding geology and physical characteristics of the habitat?  Too recreate the habitat based on the soil or geological composition of the surrounding terrestrial environment?

As we know now, the influence of factors like soil, and the presence of terrestrial materials like seed pods, leaves, and branches play a huge role in the chemical composition and appearance-of the water. It's really no different in the aquarium, right?

Like so many things in nature, the complexity of blackwater habitats is more than what meets the eye. Chemically, biologically, and ecologically, blackwater habitats are a weave of interdependencies- with soil, water, and surrounding forest all functioning together to influence the lives of the fishes which reside within them. No single factor could provide all of the necessary components for fish populations to thrive.

To damage or destroy any one of them could spell disaster for the fishes- and the ecosystem which supports them. It is therefore incumbent upon us to understand, protect, and cherish these precious habitats, for the benefit of future generations. 

And with regards to our aquarium work?

Although there may even be breakthroughs in terms of blackwater extracts and additives coming to market, there are still a lot of questions that would have to be answered before we could simply state that "X" drops per gallon of such an such a formula would yield a specific outcome. This reminds me of the reef aquarium world more an more, lol.

So, if I've made any "argument" here, it's that this stuff is every bit as much of an "art"- in terms of aquarium keeping- as it is a "science." We will, at least for the foreseeable future, have to use the data we have available and formulate a best guess as to how much of what can give us some of the impacts we are interested in for our aquariums.

We simply can't authoritatively make blanket statements like, "You need to use "X" catappa leaves per gallon in order to recreate Rio Negro-like conditions in your aquarium!" We can't simply state that you can throw in some podzolic soil and achieve blackwater, either. There are many factors in play, as we've discussed here, right?

Marketing hyperbole aside, we really are sort of...guessing.

And that's certainly nothing to be discouraged about!

We, as a community, are getting deeper into the functional aspects of blackwater, botanical-style aquariums than ever before. More light is being shed on what's going on in both our aquariums and in the natural habitats we desire to replicate. We are learning more every day about how the presence of tannins and humic substances in our aquariums is affecting the health, longevity, and spawning behaviors of our blackwater fishes.

We're learning about the challenges and realities of managing blackwater systems over the long term- understanding the good, the bad, and the dangerous possibilities that are present when we experiment with these ideas.

There is much, much more work to be done..And a lot of talented hobbyists like yourself are out there on the front lines every day, contributing to the body of knowledge that will benefit the hobby for generations!

Stay persistent. Stay bold. Stay open-minded. Stay curious. Stay disciplined...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



One of the toughest things in the aquarium hobby is to face the possibility of losing fishes. When you think about it, the idea of keeping live tropical fishes in an aquarium is pretty incredible to begin with. What we take on isn't necessarily "difficult" in many instances. The techniques have been known and shared in the hobby for generations. However, the awesome thing is that we are able to obtain and maintain these organisms in the first place, right? 

And when you add into the equation that are completely responsible for creating essentially the entire environment in which they reside, it becomes even more incredible, right? What we do is pretty special.

However, unlike keeping many other animals as"pets", like dogs, cats, hamsters, rabbits, etc., we have the unique ability to create representations- functional and aesthetic-of the natural habitats from which they come. We can do all sorts of environmental manipulations, and embrace all sorts of evolutions within their aquariums to represent aspects of their natural habitats.


And this ability brings with it a lot of opportunity to innovate, as well as the assumption of some risk.

Yeah, the process of creating, optimizing and managing a specialized aquatic habitat is subject to risk, whether we expect it or not. 


The risk that we might not have acclimated our fishes correctly to the new environment that we have created. Risk that our management of the environment may not be be as controlled, consistent, or appropriate for the long-term health of the fishes.

This is not unique to the botanical-style aquarium, of course. It's something that we run into with all types of aquariums and fish-keeping endeavors, from the most basic goldfish bowl (arrghh!😂) to the most sophisticated reef aquarium system.

Risk permeates this hobby. It's something that is almost never discussed, but it is at the forefront of almost everything do. Risk abounds. We take risks every single time we purchase fish. And the responsibility to manage the risk- to mitigate any potential bad outcomes-lies squarely on our shoulders as hobbyists.

A classic, easy example? When repurchase that new fish, we immediately have to chose whether or not we will quarantine it before placing it into our tank. If we don't, we run the risk of introducing illness to our other healthy fishes. And, when we do quarantine (yay!),we STILL risk the possibility that the fish might not make it through. That it might not eat, or that a disease (the very reason you quarantine in the first place!) may manifest itself and possibly kill the fish in the quarantine system.


When we first started Tannin Aquatics, the idea of utilizing seed pods, bark, leaves, branches and stuff  in aquariums to manipulate the environmental conditions wasn't completely unknown. Hobbyists have been doing it for generations to some extent. However, when we embarked on our mission to curate, test, and ultimately introduce new and different botanical materials into the hobby, we know it was a risk.

Some might have proven to be toxic to fishes. Some might have been collected from polluted environments that had noxious chemicals. Some might have been intended for other purposes, and sold to us by unscrupulous suppliers, who had them treated with laquers or other industrial chemicals. We found this out the hard way a few times, killing fishes in our test tanks in the process.

Horrible to lose innocent animals, but part of the challenge we accepted when we intended to become leaders in this new arena. Releasing untested materials to fellow fish keepers and killing them was not an option. We had to assume the risk of testing ourselves. Vetting of suppliers was, and continues to be, crucial. Good quality source material doesn't guarantee success- but it does mitigate some of the risk. 

When we developed techniques for the preparation of botanicals for aquarium use, it was to help mitigate some of the risks that are inherent when you place natural terrestrial materials into a closed aquatic environment.


Yet, even with the development of "best practices" and recommended approaches and technique for safely utilizing botanicals in our aquariums, we knew that there was an even bigger, more ominous risk out there...Human nature.

Yes, when I started playing with botanicals in my aquariums almost two decades ago, I made a fair number of mistakes. Sometimes, they cost the lives of my fishes.

And killing fishes sucks.


Some mistakes were caused by my lack of familiarity with using various materials. Most were caused by not understanding fully the impact of adding botanical materials to a closed aquatic ecosystems. All were mitigated by taking the time to learn from them and honestly asses the good, the bad, and the practical aspects of using them in our aquariums. 

And that meant developing "best practices" to help mitigate or eliminate issues as much as possible, even though the "practices" may not be the easiest, most convenient, or expedient way to proceed.

I KNEW that there would be people who might kill their fishes by adding lots of botanicals to their established systems without reading and following the instructions concerning preparation, cadence, and what to expect. I knew there would be people who would criticize the idea, "edit" the processes or recommended "best practices", talk negatively about the approach and generally scoff and downplay what they didn't know, understand, or do.

It's human nature whenever you give people something a bit different to play with...They want to go from 0-100 in like one day. And I knew that some of these people would go out on social media and attempt to trash the whole idea after they failed. This, despite all of our instructions, information, and pleas to follow the guidelines we suggested. 

After more than six years of running Tannin, I have pretty much identified the two most common concerns we have for customers associated with utilizing botanicals in their aquariums. Curiously, our two biggest concerns revolve around our own human impatience and mindset- not the botanical materials themselves.

The first is... preparation.

We are often asked why we don't feel that you can, without exception, just give any of your botanicals "a quick rinse" and toss them into your aquarium.

After all, this is what happens in nature, right? Well, shit- yes...but remember, in most cases, there is a significant "dilution factor" caused by larger water volumes, currents, biologically-rich substrates, etc. that you encounter in natural aquatic systems. Even in smaller bodies of water, you have very "mature" nutrient export systems and biological equilibriums established over long periods of time which handle the influx and export of organic materials.  

However, even in Nature, things go awry, and you will occasionally see bodies of water "fouled" by large, sudden influxes of materials (often leaves, grass clippings, etc.)- sometimes after rain or other weather events- and the result is usually polluted water, large algal blooms, and a pretty nasty smell! 

In the aquarium,  of course, you have a closed system with a typically much smaller water volume, limited import of fresh water, limited filtration (export) capacity, and in many cases, a less robust ecological microcosm to handle a large influx of nutrients quickly.

So you know where I'm going with this:

Fresh botanical materials, even relatively "clean" ones, are often still "dirty", from collection, storage, etc. They may have dust, airborne pollutants, soil or silt (depending upon where they were collected), even cobwebs, bird droppings, and dead insects (yuck!).

Natural materials accumulate "stuff." They're not sterile; made in some high tech  "clean room" in a factory in Switzerland, right? 

So," just giving botanicals a quick rinse" before tossing them in your tank is simply not good procedure, IMHO- even for stuff you collect from your own backyard. It's more risk to take on. At the very least, a prolonged (30 to 60 minute) steep in boiling hot water will serve to "sterilize" them to a certain extent. Follow it with a rinse to remove any lingering dirt or other materials trapped in the surfaces of your botanicals.

Now, I don't recommend this process simply because I want to be a pain in the ass. I recommend it because it's a responsible practice that, although seemingly "overkill" in some people's minds- increases the odds for a better outcome.

It reduces some of the risk.

The crew up in the cockpit on your flight from L.A. to New York know every system of the Boeing 737Max9 that they fly. But guess what? They still complete the pre-flight checklist each and every time they hop in the plane.

Because it can save lives.

Why should we be any different about taking the time to prepare botanicals? I know it sounds harsh; however, if you skip this step and kill your fishes- it's on you.


Why would you skip this, other than simply being impatient?

Could you get away with NOT doing this? 

Sure. Absolutely. Many people likely do. 

But for how long? When will it catch up with you? Maybe never...I know I'll get at least one email or comment from a hobbyist who absolutely doesn't do any of this and has a beautiful healthy tank with no problems.

Okay, good for you. I'm still going to recommend that, like I do- that you embrace a preparation process for every botanical item that you add to your aquariums.

Boiling/steeping also serves a secondary, yet equally important purpose: It helps soften and even break down the external tissues of the botanical, allowing it to leach out any remaining subsurface pollutants, sugars, or other undesirable organics to the greatest extent possible. And finally, it allows them to better absorb water, which makes them sink more easily when you place them in your aquarium. 

Yes, it's an extra step.

Yes, it takes time.

However, like all good things in nature and aquariums, taking the time to go the extra mile is never a bad thing. And really, I'm trying to see what possible "benefit" you'd derive by skipping this preparation process?

Oh, let me help you: NONE.


There is simply no advantage to rushing stuff.

Like all things we do in our aquariums, the preparation of materials that we add to them is a process, and Nature sets the pace. The fact that we may recommend 30 minutes or more of boiling is not of concern to Nature. It may take an hour or more to fully saturate your Sterculia Pods before they sink.

So be it.


Savor the process. Enjoy every aspect of the experience.  And don't you love the earthy scent that botanicals exude when you're preparing them?

And the shittiest thing? Even if you do all this prep, there is STILL risk that you will kill your fishes.


Damn, I'm not ever gonna make it as salesman, huh?

How much to use?

Well, that's the million dollar question.

Who knows? Even that is a guess and decidedly unscientific at best! 

It all gets back to the (IMHO) absurd "recommendations" that have been proffered by vendors over the years recommending using "x" number of leaves, for example, per gallon/liter of water. There are simply far, far too many variables- ranging from starting water chem to pH to alkalinity, and dozens of others- which can affect the "equation" and make specific numbers unreliable at best. 

Now, nothing is perfect.

Nothing we can tell you is an absolute guarantee of perfect results...You're dealing with natural materials, and the results you'll see are governed by natural processes that we can only impact to a certain extent by preparation before use. But it's a logical, responsible process that you need to embrace for long-term success.

It reduces some of the risk.

And, when it comes time to adding your botanicals to your aquarium, the second "tier" of this process is to add them to your aquarium slowly. Like, don't add everything all at once, particularly to an established, stable aquarium. Think of botanicals as "bioload", which requires your bacterial/fungal/microcrusacean population to handle them.

Bacteria, in particular, are your first line of defense.

If you add a large quantity of any organic materials to an established system, you will simply overwhelm the existing beneficial bacterial population in the aquarium, which will likely result in a massive increase in ammonia, nitrite, and organic pollutants. At the very least, it will leave oxygen levels depleted, and fishes gasping at the surface as the bacteria population struggles to catch up to the large influx of materials.

This is not some sort of esoteric concept, right? I mean, we don't add 25 3-inch fishes at once to an established, stable 10-gallon aquarium and not expect some sort of negative environmental consequence, right? So why would adding bunch of leaves, botanicals, wood, or other materials containing organics be any different?

It wouldn't.

So please, PLEASE add botanicals to your established aquarium gradually, while observing your fishes' reactions and testing the water parameters regularly during and after the process. Take measured steps.

There is no rush.

There shouldn't be.

It's interesting how the process of selecting, preparing and adding botanical materials to our aquariums has evolved over the time since we've been in business. Initially, as I discussed previously, it was all about trying to discover what materials weren't "toxic" in some way!

Then, it was about figuring out ways to prepare them and make sure that they don't pollute the aquarium. Finally, it's been about taking the time to add them in a responsible, measured matter.

I think our biggest "struggle" in working with botanicals is a mental one that we have imposed upon ourselves over generations of aquarium keeping:  The need to control our own natural desire to get stuff moving quickly; to hit that "done" thing...fast.

And the reality, as we've talked about hundreds of times here and elsewhere, is that there really is no "finished", and that the botanical-style aquarium is about evolution. This type of system embraces continuous change and requires us to understand the ephemeral nature of botanicals when immersed in water.

I know I may be a bit "blunt" when it comes to these topics of preparation, practices, and patience- but they are critical concepts for us to wrap our heads around and really embrace in order to be successful with this stuff. And they are absolutely tied to the idea of reducing risk to the greatest extent possible.

All caveats and warnings aside, the art and evolving "science" of utilizing natural botanical materials for the purpose of enriching and influencing the environment of the aquarium is an exciting one, promising benefits and breakthroughs that we may not have even thought about yet!

It's okay to experiment...If we are willing to accept the additional risk.

We stress these points over and over an over, because  I get questions every day from hobbyists asking if they really need to prepare their botanicals, and if it's safe to use "_____" in their tanks, etc.

This is indicative, to me, of larger problem in the aquarium hobby.

In a world where people are supposedly not able to retain more than 280 characters of information, and where there is a apparently a "hack" for pretty much everything,  I wonder if have we simply have lost the ability to absorb information on things that are not considered “relevant” to our immediate goal. I say this not in a sarcastic manner, but in a thoughtful, measured one.

I'm baffled by hobbyists who want to try something new and simply do next to no research or self-education prior to trying it.

Like, WTF?

When you read some of the posts on Facebook or other sites, where a hobbyist asks a question which makes it obvious that they failed to grasp even the most fundamental aspects of their "area of interest", yet jumped in head-first into this "new thing", it just makes you wonder!  I mean, if the immediate goal is to have "...a great looking tank with botanicals...", it seems to me that some hobbyists apparently don’t want to take the time to learn the groundwork that it takes to get there and to sustain the system on a long-term basis.

I suppose that it’s far more interesting- and apparently, immediately gratifying- for some hobbyists to learn about what gadgets or products can get us where we want, and what fishes are available to complete the project quickly.

This is a bit of a problem. It demonstrates a fundamental impatience, an unwillingness to learn, and a lack of desire to assume some responsibility or risk. The desire to pass the responsibility on to someone- or something- else when shit goes wrong.

And the reality is that it's really all on us.

When it comes to using botanicals- or, for that matter, embarking upon any aquarium-related speacialties, it's really important to contemplate them from the standpoint of reducing and accepting some risk. We, as aquarium hobbyists, are 100% responsible for the lives of the animals under our care. If we don't like the idea of accepting this responsibility, then we should consider another hobby. Simple as that.

I can talk about the "best practices" in our hobby until my face turns green. I can point out the benefits of making mental shifts and being patient endlessly. However, it's up to each one of us to accept- or reject- these ideas, and to accept the outcomes-positive or negative- of our choices about how we embrace-or reject-this stuff.

And, based on what I'm seeing and hearing, a lot of hobbyists simply don't feel that this applies to them.

Okay, I’m sounding very cynical. And perhaps I am. But the evidence is out there in abundance…and it’s kind of discouraging at times.

Look, I’m not trying to be the self-appointed "guardian of the hobby." I’m not calling us out. I’m simply asking for us to look at this stuff realistically, however. To question our habits. To accept responsibility for our actions. No one has a right to tell anyone that what they are doing is not the right way, but we do have to instill upon the newbie the importance of understanding the basics of our craft.

I'm super-proud that we've consistently elevated realistic discussions about unpopular topics related to our hobby sector. Yeah, we literally have blog and podcast titles like, "How to Avoid Screwing Up Your Tank and Killing all of Your Fishes with Botanicals" , or "There Will be Decomposition", or "Celebrating The Slimy Stuff."

If we are worried about risk, we need to take as many steps as possible to understand it. To mitigate it. Some steps are tedious. Unglamorous. Time consuming. Not very fun.

However, they are all steps that we need take to create better outcomes, and to help advance the state of the art of the aquarium hobby- for the benefit of us all.

Risk is part of the hobby. How we accept it, and take it on, is also part of the hobby. It doesn't have to be a dark cloud hanging over everything that we do. Rather, it should be a motivator, an opportunity to improve, and a means to grow.

Stay responsible. Stay curious. Stay engaged. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics 






The slow(er) road to success with fish stocking...

One of the questions which we are asked less and less these days is, 'What kinds of fishes are suitable for a botanical-style aquarium?" I think that after 6 years of pounding all of these ideas into your heads about all of the strange nuances of botanical-style aquariums, it's almost universally understood that pretty much any fishes can live in them.

On the other hand, when it comes to how we stock our tanks, nothing has really changed...however, it could. And it should, IMHO.

We spend a pretty good amount of time studying, scheming, and pondering how to create a compatible, interesting, and attractive community of fishes within our aquariums.

It's probably among the most enjoyable things that we do in the hobby, right?

As a somewhat eccentric philosopher of all things fish, one of my favorite things to ponder is stuff that we do while creating our aquariums which is- intentionally or otherwise- analogous to the factors in Nature that result in the environments and fish populations that we find so compelling.

If you're like me, you likely spend a little too much time pondering all sorts of arcane aspects of the hobby...Okay, so maybe you're NOT like me, but you probably have a rather keen interest in the way Nature operates in the wild aquatic systems of the world, and stock your aquariums accordingly.

As one who studies a lot of details about some of the habitats from which our fishes come, I can't help but occasionally wonder exactly what it is that brings fishes to a given location or niche within a environment?

Now, the first answer we're likely to proffer is the most apparent...right? I mean, they follow the food!

Fishes tend to move into new areas in search suitable food sources as part of their life cycle. And food sources often become available in habitats such as flooded forest areas after the rains come, when decomposing leaves and botanical materials begin to create (or re-activate, as the case may be) "food webs", attracting ever more complex life forms into the area.

When we create our aquariums, we take into consideration a lot of factors, ranging from the temperament and size of our fish selections, to their appearance, right? These are all important factors. However, have you ever considered what the factors are in nature which affect the composition of a fish community in a given habitat?

Like, why "x" fish is living in a particular habitat?

What adaptations has the fish made that make it uniquely suitable for this environmental niche? Further, have you thought about how we as hobbyists replicate, to some extent, the actual selection processes which occur in Nature in our quest to create the perfect community aquarium?

Now, if you're an African Cichlid lover or reef hobbyist, I'm sure you have!

Social hierarchies, spatial orientations, and allopathic processes are vital to success in those types of aquariums; you typically can't get away with just throwing in a random fish or coral and hoping it will just mix perfectly.

However, for many hobbyists who aim to construct simple "community tanks", it isn't that vital to fill specific niches and such...we probably move other factors to the forefront when thinking about possible additions to our community of fishes: Like, how cool the fish looks, how large it grows, if it has a peaceful temperament, etc. More basic stuff.

However, in the end, we almost always make selections based upon factors which we deem important...again, a sort of near-mimicry of natural processes- and how the fishes work in the habitat we've created for them.

"Unnatural selection?" Or...Is it essentially what nature's does for eons?

Oh, and what exactly is an "aquatic habitat", by the way? In short, you could say that an aquatic habitat is the physical, chemical, and biological characteristics which determine the suitability for habitation and reproduction of fishes.

Of course, these characteristics can determine which fishes are found in a given area in the wild- pretty much without exception. It's been happening for eons.

Approaching the stocking of an aquarium by determining which fishes would be appropriate for the physical characteristics of the tank is not exactly groundbreaking stuff.

However, when we evaluate this in the context of "theme", and what fish would be found within, say, an Amazonian Igarape stream or a Southeast Asian peat swamp, the idea of adding fishes to "exploit" the features of the habitat we've created is remarkably similar to the processes which occur in Nature that determine what fish are found there, and it's the ultimate expression of good tank planning, IMHO.

It's just kind of interesting to think about in that context, right?

Competition is another one of the important factors in determining  how fish populations in the wild. Specifically, competition for space, resources (e.g.; food) and mates are prevalent. In our aquariums, we do see this to some extent, right? The "alpha male" cichlid, the Pleco that gets the best cave, and the Tetra which dominates his shoal.

How we create the physical space for our fishes can have significant impact on this behavior. When good hiding spaces are at a premium, as are available spawning partners, their will be some form of social hierarchy, right?

Other environmental factors, such as  water movement, dissolved oxygen, etc. are perhaps less impactful on our community once the tank is established. However, these factors figure prominently in our decisions about the composition of, or numbers or fishes in the community, don't they?

For example, you're unlikely to keep Hillstream loaches in a near stagnant, blackwater swamp biotope aquarium, just like you'd be unlikely to keep Altum Angelfish in a fast-moving stream biotope representation. And fishes which shoal or school will, obviously, best be kept in numbers.

"Aquarium Keeping 101", again.

One factor that we typically don't have in our aquaria is predation. I know very few aquarists who would be sadistic enough to even contemplate trying to keep predators and prey in the same tank, to let them "have at it" and see what happens, and who comes out on top!

I mean, there is a lot to this stuff, isn't there?

Again, the idea of creating a tank to serve the needs of certain fishes isn't earth-shattering. Yet, the idea of stocking the tank based on the available niches and physical characteristics is kind of a cool, educational, and ultimately very gratifying process. I just think it's truly amazing that we're able to actually do this these days.

And the sequence that you stock your tank in is extremely pertinent.

I think that you could literally create a sort of "sequence" to stocking various types of fishes based on the stage of "evolution" that your aquarium is in, although the sequence might be a bit different than Nature in some cases. For example, in a more-or-less brand new aquarium, analogous in this case to a newly-inundated forest floor, their might be a lot less in the way of lower life forms, such as fungi and bacteria, until the materials begin breaking down. You'd simply have an aggregation of fresh leaves, twigs, seed pods, soils, etc. in the habitat.

So, if anything, you're likely to see fishes which are much more dependent upon  allochthonous input...food from the terrestrial environment. This is a compelling way to stock an aquarium, I think. Especially aquarium systems like ours which make use of these materials en masse.

Right from the start (after cycling, of course!), it would not be unrealistic to add fishes which feed on terrestrial fruits and botanical materials, such as Colossoma, Arowanna, Metynis, etc. Fishes which, for most aquarists of course, are utterly impractical to keep because of their large adult size and/or need for physical space!

(Pacu! Image by Rufus46, used under CC BY-SA 3.0)

Now, a lot of smaller, more "aquarium suited" fishes will also pick at these fruits and seeds, so you're not totally stuck with the big brutes if you want to go this route! Interestingly, the consumption and elimination of fruits by fishes is thought to be a major factor in the distribution of many plants in the region.

Do a little research here and you might be quite surprised about who consumes what in these habitats!

More realistically for most aquarists, I'd think that you could easily stock first with fishes like surface-dwelling (or near surface-dwelling) species, like hatchetfishes and some Pencilfishes, which are largely dependent upon terrestrial insects such as flies and ants, in Nature. In other words, they tend to "forage" or "graze" little, and are more opportunistic, taking advantage of careless insects which end up in the water of these newly-inundated environs.

I've read studies where almost 100 species were documented which feed near-exclusively on insects and arthropods from terrestrial sources in these habitats! As I mention often, if you dive a bit deeper than the typical hobbyist writings, and venture into scholarly materials and species descriptions, you'll be fascinated to read about the gut-content analysis of fishes, because they give you a tremendous insight about what to feed in the aquarium!

Continuing on, it's easy to see that, as the environments evolve, so does the fish population. And the possibilities for simulating this in the aquarium are many and are quite interesting!

Later, as materials start to decompose and are acted on by fungi and bacteria, you could conceivably add more of the "grazing" type fishes, such as Plecos, small Corydoras, Headstanders, etc.

As the tank ages and breaks in more, this would be analogous to the period of time when micro-crustaceans and aquatic insects are present in greater numbers, and you'd be inclined to see more of the "micropredators" like characins, and ultimately, small cichlids.

Interestingly, scientists have postulated that evolution favored small fishes like characins in these environments, because they are more efficient at capturing small terrestrial insects and spiders in these flooded forests than the larger fishes are!

And it makes a lot of sense, if you look at it strictly from a "density/variety" standpoint- lots of characins call these habitats home!

Then there are detritivores.

The detrivorus fishes remove large quantities of this material from submerged trees, branches, etc. Now, you might be surprised to learn that, in the wild, the gut-content analysis of almost every fish indicates that they consume organic detritus to some extent! And it makes sense...They work with the food sources that are available to them!

At different times of the year, different food sources are easier to obtain.

And, of course, all of the fishes which live in these habitats contribute to the surrounding forests by "recycling" nutrients locked up in the detritus. This is thought by ecologists to be especially important in blackwater inundated forests and meadows in areas like The Pantanal, because of the long periods of inundation and the nutrient-poor soils as a result of the slow decomposition rates.

All of this is actually very easy to replicate, to a certain extent, when stocking our aquaria. Why would you stock in this sort of sequence, when you're likely not relying on decomposing botanicals and leaves and the fungal and microbial life associated with them as your primary food source?

Well, you likely wouldn't be...However, what about the way that the fishes, when introduced at the appropriate "phase" in the tank's life cycle- adapt to the tank? Wouldn't the fishes take advantage of these materials as a supplement to the prepared foods that you're feeding them? Doesn't this impact the fishes' genetic "programming" in some fashion? Can it activate some health benefits, behaviors, etc?

I believe that it can. And I believe that this type of more natural feeding ca profoundly and positively impact our fishes' health.

I’m no genius, trust me. I don’t have half the skills many of you do but I have succeeded with many delicate “hard-to-feed” fishes over my hobby “career.” 


Because I'm really patient.

Success with this approach is simply a result of deploying "radical patience."  The practice of just moving really slowly and carefully when adding fishes to new tanks. 

It's a really simple concept.

The hard part is waiting longer to add fishes.

Wait a minimum of three weeks—and even up to a month or two if you can stand it, and you will have a surprisingly large population of micro and macro fauna upon which your fishes can forage between feedings.

Having a “pre-stocked” system helps reduce a considerable amount of stress for new inhabitants, particularly for wild fishes, or fishes that have reputations as “delicate” feeders.

And think about it. This is really a natural analog of sorts. Fishes that live in inundated forest floors (yeah, the igapo again!) return to these areas to "follow the food" once they flood.

It just takes a few weeks, really. You’ll see fungal growth. You'll see some breakdown of the botanicals brought on by bacterial action or the feeding habits of small crustaceans and fungi. If you "pre-stock", you might even see the emergence of a significant  population of copepods, amphipods, and other creatures crawling about, free from fishy predators, foraging on algae and detritus, and happily reproducing in your tank.

We kind of know this already, though- right?

This is really analogous to the tried-and-true practice of cultivating some turf algae on rocks either in or from outside your tank before adding herbivorous, grazing fishes, to give them some "grazing material." 

Radical patience yields impressive results.

It’s not always easy to try something a little out of the ordinary, or a bit against the grain of popular practice, but I commend you for even thinking about the idea. At the very least, it may give you pause to how you stock your tank in the future, like  "Herbivores first, micro predators last", or whatever thought you subscribe to. 

Allow your system to mature and develop at least some populations of fauna for these fishes to supplement their diets with. You’ll develop a whole new appreciation for how an aquarium evolves when you take this long, but very cool road.

Stay patient. Stay observant. Stay creative. Stay studious. Stay resourceful...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


It's only a "fail" if you make it one...

Part of the aquarium hobby experience is screwing stuff up.

There are so many things that we do as aquarists which involve variables beyond our control, that failure in some things is almost inevitable.

And, after a lifetime in the hobby, I will occasionally reflect back on some of the great successes that I’ve had...and on some of the many, many failures that I’ve been involved with! Failures aren’t that bad, really. In fact, they're pretty damn helpful...As the sayings goes, “Nothing is ever wasted- it can always serve as an example of what NOT to do!”


Yeah, because if you learn from them, failures or disasters are extremely valuable tools for self-education.

I was thinking about my worst-ever aquarium disasters, and, fortunately, there have not been all that many...However, the ones I have had have been notable...and very educational!

My biggest mistakes came out of my own arrogance, really. Yes, arrogance. A desire to flaunt the "rules" set by Nature. 

Usually, they were "created" when I tried to do something that disregarded simple logic (and a century of aquarium common sense), like trying mixes of fishes that were absurd, or overstocking tanks...stuff like that.

For example, from my reef keeping experience- not all that many years ago, actually- I was going to be the ONE reefer to keep several Centropyge angelfish in his reef, including a Lemonpeel, Vrolicki, Coral Beauty, Flame Angel, and Bicolor! If you don't know anything about the dwarf angelfish of the genus Centropyge, the one thing you SHOULD know is that they are very territorial, and don't generally get along with others of their own species. And mixing different species is a traditional "recipe"  for disaster.

Oh, and most of the ones I wanted to keep had a well-earned reputation for snacking on coral tissue...What could go wrong here?

This was a recipe for failure that even the most inexperienced reefer could see coming. Of course, I was "experienced", so I knew better, right?


Nonetheless, I really thought I could pull this off in a large reef with specialized aquascaping... I was convinced that it could work and that I'd be the envy of the reef aquarium world for doing so...Not only did this experiment end with some "predictable" results (a lot of nice corals getting snacked on), it resulted in 5 very ticked-off, very beaten up dwarf angels! No shit? Who would have seen that coming, right?

Just plain stupid...For some reason, I really thought that my “methodology” would pay off and that it could work...WRONG.

But hey. I did it. I failed at it. I OWN it.

I distinctly remember a dubious experiment on the side of my parents' house one summer when I was a teen, attempting to culture mosquito larvae...yeah, you know how well THAT went down!  I think that was the most mosquito bites I've ever had in one summer...

But I learned my lesson....

Or the time I tried to build my own fluidized reactor. It sounded like noble project, but the reality was that I started with a bad concept and used cheap PVC materials that didn't quite match up. Yeah, it didn’t work, and the resulting leaks and total lack of functionality reflected my DIY "skills!" It was a good thought, but really poor on the "execution" side.

Completely unlike the Angelfish fiasco, which was a “lose-lose” proposition! Nowadays, if I have the urge to do DIY, I simply break out the credit card and purchase whatever it is I was thinking of making. Aquarium equipment manufacturers LOVE me!

Another lesson learned.

Oh, or there was that time I tried to make a continuous-feed brine shrimp hatcher...Shit, do you know how LONG it takes to get brine shrimp eggs out of the water column in your tank?

A really long time.

Enough said.

However, failing- and I mean this in the most literal sense- can actually be beneficial in so many ways, especially if you share your failures publicly. Right now, somewhere out in the aquarium hobby world, there is another hobbyist contemplating one of the same absurd, disaster-inevitable ideas that you brought to life...

Perhaps it's not some huge, epic-disaster-bound system failure...Maybe, it's just something that's a bad decision; one that should be aborted on, but isn't likely to be- and the outcome is already well known in the hobby...


Maybe it's in our nature as hobbyists; we just love to tempt fate. And look, I get it...I've written on these very pages that sometimes, we need to go against the grain and try new ideas.

Even after 6 years of pushing this idea of botanical-style aquariums, we're still learning some new ideas, creating "best practices", and evolving techniques. We still make a few mistakes. And, like many hobbyists, we're still trying to get our heads around the "big picture" of the approach, which seems so contradictory to what has been passed down as "the way to do stuff" in the hobby for generations. 

It makes many people uncomfortable to take leaps of faith. And, sure, despite the successful implementation of these techniques for several years by thousands of hobbyists, there is always a chance of failure.

It's scary. It can be viewed as "irresponsible" by some. At the very least, you might question the efficacy and safety of some of this stuff.

It makes sense.

We ask you to make a lot of mental shifts accept some ideas which seem to go "against the grain" of long-held hobby "best practices" and philosophies of aquarium management.

We ask you to understand what you are doing what you are doing, and what the rationale behind the approach is.


One thing that you do get when ideas are shared like this is the benefit of the body of work; the experience- good and bad- of a large community of hobbyists who have went down this same path. The key to taking an idea from "fringe" to "best practice" is sharing. 

Sharing of mistakes made, the refinements done, and the "tweaks" that yielded consistent success.

It starts by creating a hobby culture of sharing.

Sharing of our mistakes is every bit as important as sharing our amazing successes.

So imagine, for a moment, if you do a quick “confessional” post on Instagram or Facebook about your biggest aquarium screw up, and just one hobbyist who is contemplating a similar thing stumbles on it, and then decides NOT to recreate your disaster!

Think of the savings in money, frustration, and innocent animals’ lives...It’s all good. "Failure" makes you a more successful aquarist- IF you learn from the mistake, and IF you share it with others!

It's kind of fun, too!

So, don’t hide your failures.

Discuss them.

Trumpet them from the highest mountain. Savor them. Run around, scream, share, yell at people if you must...But tell ‘em that you screwed something up...Tell them how, why, and what it was that you did to screw it up! 

Then laugh about it and feel better! Look at the absurdity of the thing you did.

Of course, some seemingly counter-intuitive ideas do work.

Sometimes, you try something that YOU think will be a mess, but your friends know will work, because they've done it many times, and have refined the idea and practices. You're a bit scared...and you do it anyways based on their ideas!  And it DOES work! Like recently, when my friend convinced me to try several male Apistos of different species in my display tank...I was like, "Dude...really?"

And he said, "Trust me."  And I did. And it was awesome!

Think about "failure" in the context of the bigger picture...

The neat thing about mistakes, screw-ups, and "failures" is that they often lead to something far, far better than whatever it was that you initially failed at. Because, if you take the time to ask yourself why it happened, and reconstruct the process, and make necessary adjustments and recalibration, you'll often find that the idea can work- just in a slightly different manner than you originally thought. 

And failures are only failures if you don't learn from them.

Even in our business, we screw up shit all the time, and usually it's our own fault. And we try to learn from them and refine our processes to make sure that they don't happen again.

In fact, I've been working on a piece on the many screw-ups we’ve made here at Tannin. It’s actually kind of funny, because there ARE so many! 

"Marketing blasphemy", you say? No. Not at all. Rather, it’s a living embodiment of practicing what we preach...

As humans, we all make bad decisions from time to time. Some are the result of pushing boundaries...others are simply bad judgement. Again, how the mistake was made isn't quite as important as learning from it is.

We will all benefit from being human, being honest, and getting through our trials and tribulations in fish keeping together. And yeah, we all have more to gain than to lose from sharing our mistakes.

Trust me.

What’s the biggest screwup- the worst mistake- that you’ve made in aquarium keeping? What did you learn from it?

Don’t be shy. Own it. Share it. Your "failure" will likely lead to others succeeding...So, it wasn’t really a failure after all, right?


Stay bold. Stay thoughtful. Stay honest. Stay curious. Stay experimental...

And Stay Wet.


Scott Fellman

Tannin Aquatics

My Fave fish for botanical-style aquariums: Some long-overdue thoughts- Part 1 of many?

Of all of the topics we cover here in "The Tint", the one we discuss the least (rather shockingly, I might add) is the fishes that we keep in our tanks! Yeahs, I talk more about fungi, sediments, decomposition, and leaf litter than I do about fishes...

And of course, when someone hit me up the other day and asked, "Scott, what are your favorite fishes for botanical-style aquariums?" I was like, "Well, shit- I never even covered that!" I mean, we should have covered that before. It's a cool topic. I'm kind of unsure why, actually.

Probably because most of the articles on this topic are kind of...oh, crap, I'll say it- just boring. Ever read one of those "Top 10" listicle thingys about fishes? They usually-well, suck. Harsh, but they're kind of boring, IMHO. I mean, they talk about the size of the fish, what it eats, and what size tank you can keep it in. I mean, helpful, but..I dunno. Boring. Stuff you can pretty much find in any aquarium-related reference. You don't come here for that, I hope... So, we'll try to cover these fishes from "a slightly different perspective", as I like to say.

So, let's hit that topic today! Okay, let's hit some of it today...my list is longer than my patience to discuss them all in one piece! And I'll try my best not to do it the boring way...

Oh, damn, I might have a bunch of fishes...but I don't think I'm gonna cover all of them today...

Give me a break- it's a start, right?

Now, here's the thing- you'll find that my fish choices are as much based upon  the habitats that they come from as they are about the fishes themselves..

Okay, so let's get this party started...

In no particular order ( well, maybe in a sort of order..):

Sailfin Characin (Crenuchus spilurus)

We've all had that ONE fish which just sort of occupies a place in our hearts and minds- a fish that-for whatever reason- bites you and never lets go, right? I think that every serious aquarist has at least one such a fish..

Here's mine...

Of course, it's also about the habitat which this fish lives in that's kept me under its spell for so long...

As a lover of leaf-litter in our natural, botanical-style aquariums, I am fascinated not only by this unique ecological niche, but by the organisms which inhabit it. I've went on and on and spoken at length about many of the microorganisms, fungi, insects, and crustaceans which add to the diversity of this environment. And of course, we've looked at some of the fishes which live there, too! Perhaps not enough, actually...

One of my all-time favorite fishes- and my absolute favorite characin is none other than the amazing "Sailfin Tetra", Crenuchus spilurus!  This is a truly awesome fish- not only is it attractive and morphologically cool-looking, it has a great demeanor and behaviors which separate it from almost every other characin out there! 

I first fell for this fish as a kid, when I saw a cool pic of it in my dad's well-worn copy of William T. Innes' classic book, Exotic Aquarium Fishes. The book that pretty much assured me from toddler days that I'd be a fish geek. I obsessed over the book before I could even read...

I was hooked from the start with Crenuchus, especially when reading about the romantic etymology of the name!  And it just seemed so "mysterious" and unattainable, even in the 1930's...well, especially back in the 1930's, but it seemed downright exotic! To this day, it's one you just don't see too much of in the hobby. And then, tying it together with my love of those leaf-litter-strewn habitats, it was a combo which I couldn't resist!

I never got this fish out of my system, and it took me like 30-plus years of being a fish geek to find this fish in real life. And, you know that I jumped at the chance..It was so worth the wait!

It's almost "cichlid-like" in behavior: Intelligent, interactive, and endearing. It has social behaviors which will entertain and fascinate those who are fortunate enough to keep it.

Now, I admit, it's definitely NOT the most colorful characin on the planet. But there is more than this fish than meets the eye.

It all starts with its most intriguing name...

The Latin root of the genus Crenuchus means "Guardian of The Spring"- a really cool, even romantic-sounding name which evokes imagery-and questions! Does it mean the "protector" of a body of water, or some honorary homage to everyone's favorite season? Not sure, but you must agree that the name is pretty cool! In greek, it's krenoychos -"The God of running waters."

Yeah. That's the shit. I mean, do Latin names get any cooler than that?

The Crenuchidae (South American Darters) is a really interesting family of fishes, and includes 93 species in 12 genera throughout the Amazon region. Most crenuchids are- well, how do we put it delicately- "chromatically challenged" ( ie; grey-black-brown) fishes, which tend to lie in wait near the substrate (typically leaf litter or aggregations of branches), feeding on insects and micro invertebrates. And the genus Crenuchus consists of just one species, our pal Crenuchus spilurus, a fish which shares habits and a body shape that are more commonly associated with Cyprinids and...cichlids!

That's just weird.

Now, the relatively subdued coloration serves a purpose, of course. These fishes live among leaf litter, root tangles, and botanical debris..in tinted water...which demand (if you don't want to be food for bigger fishes and birds) some ability to camouflage yourself effectively. 

The Sailfin is an exception to the "drab" thing, and it's remarkably attractive for a very "simple" benthic-living fish. Sure, on the surface, it's not the most exciting fish out there, especially when it's a juvenile...but it's a fish that you need to be patient with; a fish to search for, collect, hold onto, and enjoy as it matures and grows. As the fish matures, in true "ugly duckling"🐥  style, it literally "blossoms" into a far more attractive fish.

The males have an extended dorsal and anal fin, and are larger and more colorful than females. Yes, colorful is relative here, but when you see a group- you'll notice the sexual dimorphism right away, even among juveniles.

Individuals spend a lot of their time sheltered under dead leaves, branches, roots, and aquatic plants. They tend to "hover", and don't dart about like your typical Tetra would. In fact, their behavior reminds me of the Dartfishes of the marine aquarium world...They sort of sit and flick their fins, often moving in slow, deliberate motions. Communication? Perhaps.

The Sailfin feeds during the daylight hours, and spends much of its day sheltering under branches, leaves, and root tangles, and is a mid-water feeder, consuming particulate organic matter, such as aquatic invertebrates, insects, bits of flowers, and fruits- the cool food items from outside of the aquatic environment that form what ecologists call allochthonous input-materials from outside of the aquatic habitat, which are abundant in the terrestrial habitats surrounding the aquatic ones which we love to model our aquariums after.

Tucano Tetra (Tucanoichthys tucano)

You all know by now that my philosophy is to study and understand the environments from which our fishes come, and to replicate them in function and form as best as possible. It doesn't always mean exactly- but it's definitely NOT forcing them to adapt to our "local tap water "conditions without any attempt to modify them.

I have a very current  "case study" of my own that sort of reflects the execution of my philosophy.

As many of you know, I've had a long obsession with the idea of root tangles and submerged accumulations of leaves, branches, and seed pods. I love the silty, sedimented substrates and the intricate interplay of terrestrial plant roots with the aquatic environment.

I was doing a geeky "deep dive" into this type of habitat in Amazonia one evening, and stumbled upon this gem from a scientific paper by J. Gery and U. Romer in 1997:

"The brook, 80-200cm wide, 50-100 cm deep near the end of the dry season (the level was still dropping at the rate of 20cm a day), runs rather swiftly in a dense forest, with Ficus trees and Leopoldina palms...in the water as dominant plants. Dead wood. mostly prickly trunks of palms, are lying in the water, usually covered with Ficus leaves, which also cover the bottom with a layer 50-100cm thick. No submerse plants. Only the branches and roots of emerge plants provide shelter for aquatic organisms.

The following data were gathered by the Junior author Feb 21, 1994 at 11:00AM: Clear with blackwater influence, extremely acid. Current 0.5-1 mv/sec. Temp.: Air 29C, water 24C at more than 50cm depth... The fish fauna seems quite poor in species. Only 6 species were collected I the brook, including Tucanoichthys tucano: Two cichlids, Nannacara adoketa, and Crenicichla sp., one catfish, a doradid Amblydoras sp.; and an as yet unidentified Rivulus, abundant; the only other characoid, probably syncopic, was Poecilocharax weitzmani."

Yeah, it turned out to be the ichthyological description of the little "Tucano Tetra", Tucanoichthys tucano, and was a treasure trove of data on both the fish and its habitat. I was taken by the decidedly "aquarium reproducible" characteristics of the habitat, both in terms of its physical size and its structure. 

Boom! I was hooked.

I needed to replicate this habitat! And how could I not love this little fish? I even had a little aquarium that I had been dying to work with for a while. 

It must have been "ordained" by the universe, right?

Now, I admit, I wasn't interested in, or able to safely lower the pH down to 4.3 ( which was one of the readings taken at the locale), and hold it there, but I could get the "low sixes" nailed easily! Sure, one could  logically call me a sort of hypocrite, because I'm immediately conceding that I won't do 4.3, and I suppose that could be warranted...

However, there is a far cry between creating 6.2pH for my tank, which is easy to obtain and maintain for me, and "force-fitting" fishes to adapt to our 8.4pH Los Angeles tap water! 

And of course, with me essentially trashing the idea of executing a hardcore 100% replication of such a specific locale, the idea was essentially to mimic the appearance and function of such an igarape habitat, replete with lots of roots and leaf litter.

And the idea of executing it in a nano-sized aquarium made the entire project more immediately attainable and a bit less daunting. I wanted to see if I could pull off a compelling biotope-inspired aquairum on a small scale.

That's where my real interest was.

So, even the "create the proper conditions for the fish instead of forcing them to adapt to what's easiest for us" philosophy can be nuanced! And it should! I don't want to mess with strong acids at this time. It's doable...a number of hobbyists have successfully.  However, for the purposes of my experiment, I decided to happily abstain for now, lol.

And without flogging a dead horse, as the horrible expression goes, I think I nailed many of the physical attributes of the habitat of this fish. By utilizing natural materials, such as roots, which are representative of those found in the fish's habitat, as well as the use of Ficus and other small leaves as the "litter" in the tank, I think we created a cool biotope-inspired display for these little guys!

And man, I love this tank!

Being able to pull off many aspects of the look, feel and function of the natural habitat of the fish was a really rewarding experience. A real "case study" for my philosophy of fish selection and stocking.  

Green Neon Tetra (Paracheirodon simulans)

Everyone knows the Neon Tetra, Paracheirodon inessi. It's a strong candidate for the title of "Official fish of the Aquarium Hobby!" Of course, there other members of the genus Paracheirodon which hobbyists have become enamored with, such as the diminutive, yet equally alluring P. simulans, the "Green Neon Tetra." Topping out at around 3/4" (about 2cm) in length, it's certainly deserving of the hobby label of "nano fish!"

You can keep these little guys in nice -sized aggregations..I wouldn't necessarily call them "schools", because, as our friend Ivan Mikolji beautifully observes, "In an aquarium P. simulans seem to be all over the place, each one going wherever it pleases and turning greener than when they are in the wild."


This cool little fish is one of my fave of what I call "Petit Tetras." Hailing from remote regions in the Upper Rio Negro and Orinoco regions of Brazil and Colombia, this fish is a real showstopper! According to ichthyologist Jacques Gery, the type locality of this fish is the Rio Jufaris, a small tributary of the Rio Negro in Amazonas State.

One of the rather cool highlights of this fish is that it is found exclusively in blackwater habitats. Specifically, they are known to occur in  habitats called "Palm Swamps"( locally known as "campos") in the middle Rio Negro. These are pretty cool shallow water environments! Interestingly, P. simulans doesn't migrate out of these shallow water habitats (less romantically called "woody herbaceous campinas" by aquatic ecologists) like the Neon Tetra (P. axelrodi) does. It stays to these habitats for its entire lifespan.

These "campo" habitats are essentially large depressions which do not drain easily because of the elevated water table and the presence of a soil structure, created by our fave soil, hydromorphic podzol! "Hydromorphic" refers to s soil having characteristics that are developed when there is excess water present all or part of the time. 

(Image by G. Durigan)

So, if you really want to get hardcore about recreating this habitat, you'd use immersion-tolerant terrestrial plants, such as Spathanthus unilateralis, Everardia montana, Scleria microcarpa, and small patches of shrubs such as Macairea viscosa, Tococa sp. and Macrosamanea simabifoli. And grasses, like Trachypogon. 

Of course, our fave palm,  Mauritia flexuosa and its common companion, Bactris campestris round out the native vegetation. Now, the big question is, can you find any of these plants? Perhaps...More likely, you could find substitutes. 

Just Google that shit! Tons to learn about those plants!

These habitats are typically choked with roots and plant parts, and the bottom is covered with leaves and fallen palm fronds...This is right up our alley, right?

Of course, if you really want to be a full-on "baller" and replicate the natural habitat of these fishes as accurately as possible, it helps to have some information to go on! So, here are the environmental parameters from these "campo" habitats based on a couple of studies I found:

The dissolved oxygen levels average around 2.1 mg/l, and a pH ranging from 4.7-4.3. KH values are typically less than 20mg/L, and the GH generally less than 10mg/L. The conductivity is pretty low. 

The water depth in these habitats, based on one study I encountered, ranged from as shallow as about 6 inches (15cm) to about 27 inches (67cm) on the deeper range. The average depth in the study was about 15" (38cm). This is pretty cool for us hobbyists, right? Shallow! I mean, we can utilize all sorts of aquariums and accurately recreate the depth of the habitats which P. simulans comes from!

We often read in aquarium literature that P. simulans needs fairly high water temperatures, and the field studies I found for this fish this  confirm this.

Average daily minimum water temperature of P. simulans habitats in the middle Rio Negro was about 79.7 F (26.5 C) between September and February (the end of the rainy season and part of the dry season). The average daily maximum water temperature during the same period averaged about 81 degrees F (27.7 C). Temperatures as low as 76 degrees' (24.6 C) and as high as 95 degrees F (35.2 C) were tolerated by P. simulans with no mortality noted by the researchers.

Bottom line, you biotope purists? Keep the temperature between 79-81 degrees F (approx. 26 C-27C).

Researchers have postulated that a thermal tolerance to high water temperatures may have developed in P. simulans as these shallow "campos" became its only real aquatic habitat.

The fish preys upon that beloved catchall of "micro crustaceans" and insect larvae as its exclusive diet. Specifically, small aquatic annelids, such as larvae of Chironomidae (hey, that's the "Blood Worm!") which are also found among the substratum, the leaves and branches. 

Now, if you're wondering what would be good foods to represent this fish's natural diet, you can't go wrong with stuff like Daphnia and other copepods. Small stuff makes the most sense, because of the small size of the fish and its mouthparts.


This fish would be a great candidate for an "Urban Igapo" style aquarium, in which rich soil, reminiscent of the podzols found in this habitat is use, along with terrestrial vegetation. You could do a pretty accurate representation of this habitat utilizing these techniques and substrates, and simply forgoing the wet/dry "seasonal cycles" in your management of the system.

There are a lot of possibilities here. 

One of the most enjoyable and effective approaches I've taken to keeping this fish was a "leaf litter only" system (which we've written about extensively here. Not only did it provide many of the characteristics of the wild habitat (leaves, warm water temperatures, minimal water movement, and soft, acidic water).

As you may recall, I utilized that particular setup as a "test bed" for my "internal food production" theory- not adding any supplemental food to the tank, and the little P. simulans simply thrived. They were active, colorful, and fat- which is a big "stretch" for a little fish! And there were two distinct spawning events in this tank!


So, maybe you've noticed a pattern to my love of certain fishes...so much is based upon the habitats that they come from. My love for the fishes was amplified when I studied and learned more about the unique habitats from which each of these fishes come. The idea of recreating various aspects of the habitat as the basis for working with these fishes is irresistible to me!

Diptail or Brown Pencilfish (Nanostomus eques

This one really should have been the top choice if I were doing it in order. I LOVE everything about this fish. Well, almost everything.

Honestly, if a fish could earn the moniker "cool", this little guy would be it. It's absolutely not an overstatement to declare that these Pencilfishes have distinct personalities! They're not "mindless-drone, stupid schooling fishes", like some of the Tetras. (Sorry, my homies...Love ya' lots, but alas- you have no individual personalities...😂)

They are proud members of the family family Lebiasinidae. It was first described in 1876 by the legendary ichthyologist, Franz Steindachner. In fact, it was one of the first members of the genus Nanostomus to be discovered and described by science.

Cool, but that's not my main reason for loving this fish. There's a bunch of unique aspects to this fish's behavior which I find enormously compelling.

The Latin name of the species, eques, means "knight", "horseman", or "rider", in reference to this species’ unique oblique swimming angle. 

Ah, that "oblique swimming angle" thing. Yeah, they swim at an angle of about 45 degrees facing upwards. This angle is thought to give them an advantage in feeding. They see insects and such that fall from overhanging vegetation better than their horizontally-oriented buddies do. They get more food that way. Simple.

(Image by Fajoe, used under CC BY-SA 3.0) 

What I really love about these fish is that they are incredibly curious and obviously intelligent, checking out just about anything which goes on in their aquarium. You get the feeling when observing them that they are acutely aware of their surroundings, and once acclimated, are pretty much fearless. A fellow hobbyist once told me she thinks they're the freshwater equivalent of Pipefish...and that sounds about right..I agree with that 100%!

They're sociable, incredibly "chill" fish. Now, the thing about their ability to adeptly feed on allochthonous input into the aquatic environment makes them easy to feed. And it also gives you some clues as to the habitats they come from. Places where the food comes from the surrounding terrestrial environment. 

Foods from the surrounding environment, such as flowers, fruits, terrestrial insects, etc. These are extremely important foods for many fish species that live in these habitats. We mimic this process when we feed our fishes prepared foods, as stuff literally "rains from the sky!" Now, I think that what we feed to our fishes directly in this fashion is equally as important as how it's fed.

The environments which provide this food abundance also provide lots of opportunities to replicate in our aquariums. I love that about this fish. They come from really cool, really inspiring habitats.

They are also really adept at picking on epiphytic materials in their botanical-style aquariums. It's an observation I've made many times with these fish.

Yeah, they seem to spend a large amount of time picking at biofilm and other material adhering to botanicals, and specifically, wood. They engage in this activity almost constantly throughout the day (between feedings, of course!). I am convinced that they are likely not specifically targeting the biofilm directly; rather, I think that they're looking for tiny crustaceans and other life forms that live in the matrix.

Nonetheless, their picking distrubs the films and puts it into suspension, where it can more easily be removed by filtration. This was an unexpected "plus" of this most beloved group of fishes. Now, I must warn you, biofilm haters- you shouldn't even consider Pencilfishes as a biofilm "control mechanism", but I suppose that to you heathens, the "collateral benefit" is nice.

They are very aware, very adept feeders...Always ready to pounce. 

What's the thing I don't like about these fish?

Oh, they can be a bit skittish. Like, chill as they are, "stuff" just freaks them out.

They will, for seemingly no reason, launch themselves out of your open-top aquarium (well, those are the only types I keep...) with tremendous agility-sometimes landing a few inches away in the tank...Other times, completely leaving the tank, and well- usually this results in a very dried-out Pencilfish!

I guess the oblique swimming angle facilitates them reaching "escape velocity" rapidly. You get the feeling that they're always in "standby for launch!" mode. Like, full-on "defcon-5" mode.

Maybe, because they're always looking UP- the slightest disturbance from BELOW triggers a launch. I don't know, but it's as good a theory as any. And a 3-inch launch gets you away from a potential predator. A 6-inch launch lands you on the floor... Damn, a good adaptation for protection, this "launching" thing. But, like, who really wants to eat a Pencilfish, right? I guess the Pencilfish don't know that...They just jump. Millenia of genetic programming can't be overcome easily!

It sucks, but it's the downside to keeping them in open-top tanks. Lots of twisted branches and even floating plants DO help limit some of this "carpet surfing" behavior, but it's not a 100% perfect solution. I admit, These guys have, in the past played a central role in some of those "And then there were none" disappearing fish sagas that I've experienced over the years.

So, if you can keep them in a low- traffic area, employ lots of branches, and maybe some floating plants...maybe you'll avoid this.

I mean, these methods also occasionally work with Hatchetfishes...another fave of mine, but almost too suicidal, even for me. And that's why they are not in my top 10 list, if you're wondering..

Okay, I could probably do a top 10, or even a dozen- fave fishes, but I'd be writing all day on this topic. Honorable mention- The Checkerboard Cichlid (Dicrossus filamentosus)... My "go-to" cichlid for botanical-style tanks...I love them- even over Apistos...And, as one of my friends told me, "Of course you do Scott- they're fucking brown!" 

Damn, my friends really know me well, huh?

Just try them in your next botanical-style aquarium. You won't regret it.  Maybe we'll deep dive in the "Fellman style" on these guys next time...

Okay that's a start... I think I can safely employ the great line used by one of the aquarium hobby's great saltwater fish experts, Scott Michael, who, upon discussing such-and-such a fish would simply declare in a deadpan manner, "If you don't keep these fish, you're stupid.." 

How can you argue with THAT kind of assertion? I totally relate to that. Well, shit- you asked me what my faves are...you knew I'd have some strong feelings about them, huh? 😆

Anyhow, I hope this little start gives you a look into the unorthodox way I think about the fish I select for my aquariums: So much of it is about studying a habitat I love, and then researching what fishes are found in it- and why. Then, creating the habitat for them. Like, "habitat-first."  Totally works for me.

I hope it works for you too!

Until Next time...

Stay thoughtful. Stay curious. Stay bold. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics