March 19, 2021

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