Big Thoughts on a Tiny Tetra- and the "difficulty" of working with some fishes...

After a lifetime in the hobby, I tend to find myself continuously drawn to fishes which, at first glance, aren't all that rare, or even "challenging" to keep...yet, somehow are seldom kept in conditions which they have adapted to live under for eons.

Here's a favorite example:

Everyone knows the Neon Tetra, Paracheirodon inessi. It's a strong candidate for the title of "Official fish of the Aquarium Hobby!"  This fish is inescapable...almost universally recognized by even non-aquarium-hobbyists.



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 moniker of "nano fish!"

You know, a little fish that you could keep in groups in a relatively small tank. Or, for that matter- a LARGE group in a LARGER aquarium! 

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 little fish is a real showstopper who it's in peak health! 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)

Are you thinking what I'm thinking? 

Yeah, the potential exists to create a really realistic functional representation of these habitats (a' la "Urban Igapo") with soils, plants, and a little bit of research.

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. 

I can think of a few already.

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? We've been workin g with these materials for years! 

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). We're talking aquarium-type depth! 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 do 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. simulanswith 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 podzolic soils found in this habitat, along with terrestrial vegetation. You could do a pretty functionally 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)- it looked pretty cool, too! 

And kind of forged some new hobby ground, at least aesthetically speaking, with a defacto "minimalist" aquascape! 

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!


A few general thoughts...

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

It becomes obvious to me, when I really start looking at things analytically, that my favorite fish choices seem to reflect a preference for specific habitats or ecological niches. Almost all of my faves tend to come from smaller tributaries and streams, with moderate to minimal current or water movement. These habitats are typically filled with leaf litter, branches, and submerged root systems. 

Many of my favorite fishes come from flooded forests (no surprise there..), or other seasonally-inundated habitats, and have specialized feeding, spawning, and foraging habits as an adaptation to these environments. Most are dimly lit, devoid of aquatic plants, with deeply-tinted water and lots of overhanging terrestrial vegetation. 

Most of them feed on allochthonous inputs (stuff that comes from outside the aquatic environment) like insects, small fruits, and flowers. Some display unusual dietary preferences, such as eating detritus, fungal growths, or lignin from submerged wood and roots. Pretty much all of them spend large amounts of time foraging.

Another common denominator of these fave fishes is that they are intimately tied to their environments. They move within, or migrate among similar habitats throughout most of their lives. As aquarium fishes, they categorically seem to do better long term when kept in tanks which replicate, to some degree, the function and form of their natural habitats. These aquatic habitats are profoundly influenced by the terrestrial habitats which surround them.

As a botanical method aquarium enthusiast, you'll get to take a good, serious look at the elegance and function of these amazing natural ecological niches, which often go unnoticed by all but the most astute observers in the wild...right from the dry comfort of you own home.

A pivotal lesson- one that made me fundamentally reconsider how to create aquariums, manage them, and work with all sorts of fishes came from studying the habitats from which our fishes come. 

And after studying these habitats, I've sort of came to a simple conclusion- one that makes keeping all sorts of fishes much easier than we have commonly believed:

Meet their needs. Not yours.

It's pretty straightforward.

Despite all of this, and after a lifetime in the hobby, I say, somewhat confidently that there are no "difficult" fish. 

Here's why:

It's not that a fish is inherently difficult...It simply means that we as hobbyists, if we want to be successful with a species, need to meet its needs. We need to make the effort to study its specific requirements, the habitat from which it comes from, it's nutritional needs, and its life cycle.  

We need to find out how to obtain the fish from sources which have properly handled it along the chain of custody from stream to store. We have to do a little research- and that sometimes means bypassing the fish-world drivel (like this blog!) and slugging it out on Google scholar, Fishbase, ResearchGate, and other academic sources.

To many hobbyists, that's difficult.

The fish, however, is not.

Difficult tasks, like, I don't know, landing a man on the fucking moon, require us to solve literally thousands of problems and challenges, accumulate resources, and to create hardware, practices, and procedures to accomplish the goal.

And as we know, even landing man on the moon isn't impossible, right?

We landed a man on the moon back in 1969 because we decided that we wanted to do it, broke it down into a series tasks and stages (projects Mercury, Gemini, Apollo), put the effort in, overcame our mistakes and failures...and went for it.

So, while trying to keep and breed, say, Indostomus paradoxus might seem like a real problem, is there a problem here, really?  Sure, on the surface, it seems like a "poster child" for "difficult", right? It's a tough to obtain, small, relatively timid fish with a tiny mouth and "specialized" feeding requirements.

Yet, break it down for a second:

It's hard to find, because there isn't a ton of demand for it. Yet, lots of people have kept and bred them over the years...Want some? Hound your suppliers, leave posts on the forums, hit up Google. DO the work. You'll find SOME, trust me. It might take a while, but you WILL find them.

The fish comes from swamps and places with muddy, soft clay-filled substrates filled with decaying leaf litter and such. Well, shit, we make a damn good soft, clay-filled muddy substrate, right?


 So, there are ALWAYS things you can try- avenues you can take- to attempt to accommodate a so-called "difficult" fish, right?

You just have to WANT to.

To me, "difficulty" in the aquarium context simply means "how much do you want it?"

How much do you want it?

How many challenges do you want to meet? How patient are you? How far will you push?

Are you up for the challenge? 

Ask yourself.

Stay persistent. Stay diligent. Stay tenacious. Stay patient...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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