Who eats what...and where? Thoughts on embracing "the whole picture" of our fishes' natural habitats in our aquariums.

Today's installment is one of those sort of meandering, perhaps choppy amalgamations of ideas, cobbled together with my typical fish-geek enthusiasm; heavy on facts, and heavier on pontificiation and speculation! 

However, I think you might like this. It's a sort of summary of what's been on my mind lately about botanical-style aquariums.

As you know, I’m pretty much an uber nerd about almost any arcane aquarium related subject. And of course, part of my regular “course of study” takes me well outside of the aquarium world. In fact, most of the best insights I have obtained on tropical fishes and the environments from which they come are derived from scholarly articles.

And these scholarly articles can give you a ton of information about not only the fishes- but about the environments from which they come. And when we combine this information with what we already know from our experience with keeping them in aquariums, the possibilities to refine our work to create more unique, imaginative, and "functionally aesthetic" aquatic displays are too numerous to mention.

I think that we as aquarists should investigate more carefully and thoughtfully some of the more subtle, yet potentially very important characteristics of the habitats from which our fishes come. Stuff which we may not have thought much about previously- like the turbidity of the water, the density and composition of the substrate, and the amount of water movement in a given habitat.

Did you catch that last one? Many fishes are found in specific types of water-movement-dynmaic habitats. There are two main classifications:

Lentic ecosystemswhich are stationary or relatively still water habitats, and Lotic ecosystems, which involve flowing waters, such as streams and rivers... Lentic ecosystems are usually habitats such as ponds, lakes, pools, and wetlands. Liek those flooded Pantanal meadows and flooded forests which we obsess over around here!

Again, when you're looking at the environments from which our fishes come from in a wholistic sense, you start thinking about more than stuff like the abundance of branches, rocks, leaves, and stuff like that. You start thinking about the composition of the substrates, the color and or turbidity of the water, and other factors which we as aquarists likely haven't paid as much attention to over the past century.

There is so much you can learn by diving deeper and detaching yourself from thinking about stuff fro ma hobby perspective for just a bit.

For example, I love reading about the dietary preferences of many of the fishes we keep- or wish to keep- in our botanical-style/blackwater aquariums. Why? Well, for one thing, when you know what the fishes eat, you get a good picture of how they live- and where!

Interestingly, many of my fave fishes (characins and other small guys) have diets which consist largely of stuff like “insect larvae, sponges, Bryozoa, algae and detritus”- all items which are found in their preferred environments... and in botanical- style aquariums, right?


I think it's important that we look at our botanical-style aquariums not just as some unique aquascape- which, of course, they are- but as a closed microcosm- a miniature environment featuring a variety of organisms all interacting with each other in a manner which can benefit the system as a whole. If we assemble our system based on this kind of thinking, the possibilities for creating a more functional habitat is increased.

And it often starts with food.

Feeding is a fundamental part of the life of our fishes, and it literally determines who lives where, and how. And examining the diets of our fishes can give us amazing clues about how to design a more appropriate and functionally realistic aquatic habitat for them, can't it?

Of course!

So, the idea here is that setting up a botanical-style aquarium can be based around not only the environmental requirements of your target fishes (ie; water chemistry, temperature, light intensity, and physical surroundings)- it can be built around other factors, such as the availability of food sources.

If you look at some specific types or families of fishes, you can get an idea of where they live by considering what they eat.

For example, some of my fave fishes, the Pencilfishes, have very specific dietary preferences- and this dictates not only where they live, but how they live in the water column of their habitats. Pyrrhulina feed on insects, and inhabit the upper portion of the water column. Fishes in the genus Nannostomus feed on benthic invertebrates, and tend to live lower down in the water column.

And then there are those other guys...

Everyone knows about the Piranha and it’s penchant for eating flesh of other fishes. It’s relatives in the family Serrasalmidae, Colossomoa, Metynnis, and Piractus, consume a more herbivorous diet, like fruits, seeds, leaves, and occasionally, flowers. Some species only consume the whole fruits, defecating large numbers of seeds in the process—functioning as highly effective seed dispersers for wide range of trees in the flood plains which they inhabit. 

This is fascinating. These fishes are an integral part of the habitats in which they reside- and they help shape the future of it with their eating habits!

Some are so specialized that they forage almost exclusively on aquatic plants (such as plants in the family Podostemaceae) and consume the leaves, seeds, and flowers of these plants! 

Interestingly, the whole group is very sensitive to noise and splashing in the waters where they live. Piranhas respond to the noise thinking that there are animals or fish prey around, where the frugivores, like Colossoma hear a splash and think, “Ahah! a fruit just fell into the water!” ( okay, they may not THINK that, but they do respond to the noise looking for fruits!

Some in the family, such as Myloseoma, feed on all sorts of stuff as they can find it, ranging from seeds, fruits, flowers, and algae to stuff like spiders, cockroaches, beetles, and ants. They’re even known to eat monkey feces! Okay, I'll leave that one alone- but you get the idea...they're hardly picky, right?

I mean, monkey shit? Yeah.

Durophagous fish eat hard shelled or exoskeleton bearing organisms- crabs, mussels, snails, etc. Usually, these kinds of fishes are found in lakes or larger rivers, where water conditions and flow characteristics tend to favor the presence of those food sources.

And of course, fishes often move throughout their habitats seasonally, following the food. 

A few of my favorite fishes, such as the awesome Crenuhus spilurus, the "Sailfin Tetra"- have broad dietary preferences. It's been observed that the fish feed freely during daylight hours, and grab most of their food as it falls though the water column. What do they eat? Well, this is interesting to me: A lot of particulate matter that sinks; specifically, stuff like fruits, terrestrial insects, and very young tadpoles made uo the bulk of the stomach contents in a recent (2016) study of this fish.

So, yeah, a typical consumer of...allochthonous materials (stuff which comes from the environment surrounding the aquatic habitat)!

Now, we've talked extensively in several blog posts over the past couple of years about the idea of allochthonous input (literally, food from the sky, lol) and how it impacts the feeding habits of many fishes, as well as their social and behavioral habits, and what could loosely be referred to as their "migratory patterns."

It's long been known that fishes which inhabit the flooded forest floors (igapo) of Amazonia, for example, tend to literally "follow the food" and move into new areas where greater feeding opportunities exist, and will even adjust their dietary preferences seasonally to accommodate the available foods.

In this instance, it typically means areas of the forest where overhanging vegetation offers falling peices of fruit, seeds, nuts, plant parts, and the occasional clumsy insect, like an ant, which falls from the branches of said vegetation. So, here is where the idea gets interesting to me: Wouldn't it make a lot of sense to create a biotope-style aquarium which not only represents the appearance of the habitat, but also replicates, to a certain extent, the function of it?

Of course it would!  (Surely, you wouldn't have expected any other answer from me, right?)

In this case, the "function" being the presence of allochthonous materials! Well, yeah. we've just described our botanical-style aquariums in (pardon the expression) a nutshell! Our tanks are replete with lots of terrestrial plant material (ie; botanicals, leaves, and wood), upon which our fishes and other aquatic animals will forage and even consume them directly over time.

I asked myself which materials would most realistically represent some of these items, and sort of came up with a list of my personal favorites. Now, obviously, you can utilize other stuff- and in terms of actual foods, you might even want to experiment with little appropriately-sized bits of fruit for fishes to consume directly! (back to that shortly)


Here are the botanicals that I think would best serve to represent some of the allochthonous materials we see in these forests:

Dysoxylum pods

Calotropis pods

Banana Stem Pieces

Pyrifolium pods

So, yeah, you could add an assortment of these and/or other materials to your tank, with the sole intention of utilizing them to represent the materials which fall off the trees and are directly consumed by some fishes and shrimp. Because of their physical structure, these selections tend to soften up fairly quickly after submersion, and are also pretty good at "recruiting" biofilms, which serve as a significant supplemental food source for a variety of fishes.

Utilizing appropriate fruits like finely-chopped açaí berries, blueberries, strawberries, Passion Fruit, and bananas to represent the fruits of the forest, is something I've played with for a long time with my Tetras and other characins. Believe it or not, they'll actually consume these foods directly, and I've also used flax seed and chia seeds for this purpose as well. 

Passion Fruit ( Image by fir0002   Used under GFDL 1.2)

Many of these will represent the fruits of the Amazon rain forest, such as Camu Camu, Cupuaçu, Passion Fruit, aguaje (fruit of the Mauritia Plam), If you search health food stores and speciality fruit/produce vendors, you might find fresh or packaged versions of some of these unique fruits, or you could use the more commonly available substitutes mentioned above.

I could imagine changing up the diet of your fishes seasonally, along with ideas like environmental manipulations and "power dosing" botanicals into the aquarium to represent the "high water" season, to see how this impacts behavior, health, and spawning activities of your fishes from this habitat. We have the technology. We have the knowledge...and we have the food!

Studies of blackwater communities showed that, during these cycles, a greater diversity of fishes exists there. Many species were found to be specialized feeders. Fish, detritus and insects were the most important food resources supporting the fish community in both high and low water seasons, but the proportions of fruits, invertebrates and fish were reduced during the low water season.

Are there some "takeaways" here for us fish geeks?

Hmm, what this means to us is that fish sort of "follow the food", right? And that the "seasonal availability" of some food sources actually dictates overall fish behavior. 

And then, there's our old friend...detritus. 

"detritus is dead particulate organic matter. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose or remineralize the material." (Source: The Aquarium Wiki)

Shit, really?

It's one of our most commonly used aquarium terms...and one which, well, quite frankly, sends shivers down the spine of many aquarium hobbyists. And judging from that definition, it sounds like something you absolutely want to avoid having in your system at all costs. I mean, "dead organisms" and "fecal material" is not everyone's idea of a good time, ya know?

Yet, when you really think about it, "detritus" is an important part of the aquatic ecosystem, providing "fuel" for microorganisms and fungi at the base of the food chain in tropical streams. In fact, in natural blackwater systems, the food inputs into the water are channeled by decomposers, like fungi, which act upon leaves and other organic materials in the water to break them down. 

And the leaf litter "community" of fishes, insects, fungi, and microorganisms is really important to these systems, as it assimilates terrestrial material into the blackwater aquatic system, and acts to reduce the loss of nutrients to the forest which would inevitably occur if all the material which fell into the streams was washed downstream!

That sounds all well and good and grandiose, but what are the implications of these processes- and the resultant detritus- for the closed aquarium system?

Well first off, let's admit that the stuff  just doesn't look that nice to most of us, and that's partially why the recommendation for a good part of the century or so we've kept aquariums is to siphon it the hell out! And that's good advice from an aesthetic standpoint- and for that matter, from a husbandry standpoint, as well.Excessive amounts of accumulating waste materials can lead to increased phosphate, nitrate, and other problems, including blooms of nuisance algae.

Emphasis on the word "excessive" here...(which begs the question, "What is "excessive" in this context, anyways?)

Most hobbyists don't have the time, inclination, or optimized system set up to take advantage of a small accumulation of this stuff. However, with the importance of detritus in creating food webs in wild leaf litter communities, which we are now replicating in aquariums, could there actually be some benefit to allowing a little of this stuff to accumulate? Or at least, not "freaking out" and removing every single microgram of detritus as soon as it appears?

I think so. Really.

Is this another one of those long-held "aquarium truisms" that, for 90% of what we do is absolutely the correct way to manage our tanks, but which, for a small percentage of aquarists with the means, curiosity and inclination to experiment, could actually prove detrimental in some way?

Okay, I know that now a bunch of you are thinking, "This guy IS nuts. Letting detritus accumulate in an aquarium is bad news. A recipe for problems- or worse. And not only that, he has no idea of the implications of what he's suggesting."

Well, as far as the first part of your thought- Yeah, I could be a bit "crazy." On the other hand, I think I do have some idea of the implications of what I'm postulating here. First off, remember, I'm not suggesting that everyone throw away their siphons and just allow shit (literally!) to accumulate in their aquarium substrate in the interest of creating a "food web."  

No sir.

What I am curious about is if there is some benefit in a botanical, blackwater system, of encouraging a bit more fungal and microbial growth, utilizing, among other things, the organic detritus that inevitably is produced in a well-managed. well-populated aquarium.  I mean, if you're doing water changes and removing uneaten food, dead fishes, aquatic plant leaves, etc., you're already significantly reducing the "food inputs" available to the organisms on the low end of the food chain, right?

In a typical aquarium, well-maintained with regular water changes and removal of detritus, our fishes are almost 100% dependent upon us to provide food, right? So, why not promote some of this detritus to accumulate- as part of the "supplemental food" for your fishes. I've done this several times now with great success, and no longer see it as some bold experiment or stupid stunt. 

I think it's a valid practice if understood and executed upon correctly.

Once again, we're questioning our age-old practices not to be a pain in the ass...rather, to see if what we're doing IS truly the best practice, and to see if there might be a better way. A more natural way. One which ties in with the way we manage our aquariums as a whole- botanical-style or otherwise. All of these things are potentially interrelated, and all of them are worth taking a look at with a fresh perspective. 

The big winners here: The fishes, the hobby, the hobbyist..and of course, the natural habitats-because if we understand how fishes and their habitats are intertwined and related, we will have a better understanding of the need to protect and preserve these priceless ecosystems for future generations to enjoy.

As usual, today's

rambling discussion likely leads to more questions than answers. However, some of these questions- which address some of the most fundamental, long-held beliefs and practices in aquarium-keeping, might help us make not only more "mental shifts", but true breakthroughs as we rediscovery the utility of the elegant, yet "complex simplicity" that nature has engineered over the eons.

Embracing- not fighting- nature in a more complete sense just might be "the next big breakthrough" in aquarium keeping. 

And it all starts with thinking about the environments of our fishes, and how to replicate them in the most comprehensive, realistic, and functional way possible.

We've got this.

Stay excited. Stay observant. Stay curious. Stay dedicated. Stay creative. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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