The little Tetra that can..A deeper dive.

One of the things I enjoy most in the aquarium hobby is studying the ecology of the natural habitats of our fishes. I've found over the years that you can find out so much about the fish by understanding a bit about where it comes from. 

When it comes to characins, there are few more widely known and loved in the hobby than the Neon Tetra, Paracheirodon inessi. This little fish has been the "gateway drug" for generations of tropical fish hobbyists, providing a colorful, exotic look into Nature's magnificent creations.

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 ( also 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 all or part of the time. 

(Image by G. Durigan)

So, if you really want to get hardcore in 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...This is right up our alley, right?

Of course, if you really want to be a "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. T

he 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? I mean, we can utilize all sorts of aquariums and accurately recreate the depth of the habitats which P. simulans comes from!

Now, as aquarists, we often hear 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!


I'm preparing for a second run at replicating this fish's habitat, this time with a different substrate and a "root tangle" approach using Melastoma Root and "Borneo Root". I am really looking forward to seeing if there are any behavioral differences with a more densely packed hardscape configuration, as opposed to the completely open "no scape" that the previous version offered.

Now, the pH issue is something we all have to think about and experiment with if we really want to go as accurately as possible.

I know of few hobbyists who have ventured into the "sub 5" range with pH, so that's a real interesting challenge and approach; not for the feint of heart. It can be done, it simply requires a greater understanding of water chemistry and the techniques and materials designed to get you there.

This is currently the realm of super-experienced, highly experimental hobbyists, who are perhaps trying to unlock secrets of very demanding fishes, such as Altum Angels and others, which are known to come from and thrive in pH levels below 5.0. And, to achieve and maintain such pH levels, we're learning that the careful administration of acids, and the application of other exotic and scary-sounding techniques is required.

And the management of low pH systems, with the additional benefit of humic substances provided by botanicals, is a real "frontier" in the hobby. Even in the greater context of the blackwater aquarium world, it's seen as such. It can be challenging. But it's not the frightening sideshow it once was.

I mean, it sounds a bit scary, right? What exactly is the challenge here, besides getting the water to your desired target pH?

Understanding water quality management and the way in which denitrification occurs in closed systems in very low pH is challenging. On the surface, it seems really scary and daunting. I can't help but believe that- like so many things in the aquarium hobby-it's more of a function of the fact that we haven't done much with this in the past, and we simply don't have a "path" to follow just yet. We need to understand a different class of organisms which "run the cycle" in this environment, and how to manage them.

I do know that "Culture", our Purple Non Sulphur bacteria innoculant (a colony of Rhodopseudomonas palustris) is perfect for the management of the nitrogen cycle in low pH aquairums, even competing with Archaens in this environment. Real "extremophiles" which can help with part of the equation here!

Pushing the limits a bit...trying different techniques, enriched by our understanding of the wild habitats of our fishes. Helping the hobby advance. Is't this a delicious challenge? 

This is one of the reasons why I have had a near-obsession with attempting to recreate, to some extent, as many of the physical/environmental characteristics of their wild habitats as possible for the fishes under my care. All the while, realizing that, although they will be residing in a closed system with many physio-chemical characteristics similar to what they have evolved to live under, it's not a perfect replication, much though I might want it to be, and being of the opinion that replicating "some"of these characteristics is likely better than replicating "none" of them, I say "Go for it!"

An arrogant assumption on my part, I suppose. I mean, like every one of you, I'm fully responsible for the animals which I keep. And I take a certain degree of pride in that. I want the best for them.

That being said, I'm personally not in that mindset of having to be absolutely "hardcore" about being 100% accurate biotopically, in terms of making sure that every leaf, every twig, every botanical is from the specific habitat of the fishes which I keep. I do respect aquarists who do, however.

But that's not me. Rather, I place the emphasis on providing a reasonably realistic, "functionally aesthetic" representation of the habitat form which they come, with aquascaping materials, layout, and environmental parameters configured to match, as close as possible to the parameters in the wild. It's not a perfect science. It's a challenge sometimes, too. 

A big challenge- and a fun one- from such a little fish! The rewards are many for those who meet the challenge.

Stay resourceful. Stay creative. Stay studious. Stay inspired. Stay diligent.

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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