Following the fishes...

We talk a lot about diversity in our use of botanicals in aquariums, and I know I presented, on a number of occasions, my ideas about not going too crazy with too many different varieties of botanicals in one aquarium. Of course, this is based on my opinion, and not on any specific observation I've made.

One thing that has been studied- fairly extensively, I might add- is the diversity of fish species in specific ecological niches and locales. I spend a fair amount of time perusing scientific literature online, attempting to ferret out little nuggets of information which might be applicable to thew or we do as hobbyists. I've found lots of cool information about the habitats, water chemistry, and ecology of the regions I'm into, as well as some really cool studies on fish population composition and species diversity in some of these niches.

I think we as hobbyists could get some interesting ideas about how to stock our aquariums from perusing some of these studies. Knowing what fishes are found where is beneficial more than for just winning a biotope aquarium contest.'s interesting information to have because it can give us insight into the types of food resources, water conditions, and physical structures of the habitats from which they come...And that could enable us to create and populate more "structurally functional" aquariums for our fishes- which might be the key to unlocking secrets about their husbandry and reproduction!

And it starts with surveys of what is found in a given area...

For example,  a study I found regarding the igarape of the Rio Acre area in Brazil, conducted over about a year in a fairly sizable sampling area of the region yielded some neat stuff. It's a pretty typical habitat in this area, under the usual pressures from man's activities, which have resulted in some loss of vegetation which is an important component of these inundated forest floor habitats.

Nonetheless, the richness of species in this one are was significant! The study found 94 different species in 24 families. What was most interesting to me was the composition. We're talking about the highest percentage of species collected being characins (around 45 different species). Next most common group was Siluriformes- with 33 species of catfishes, such as Ancistrus, Corydoras, Farlowella, and Otocinculus, among others, being represented. Next was the Gymnotiformes- Knifefishes- with 8 species, including the cool Eigenmannia virescens (a species I hope we see more of!), followed by the Perciformes-Cichlids! The cichlids in the region were represented by families familiar to hobbyists- Crenicichla, Apistogramma, Aequidens, and Satanoperca.

So, if we were to take this information literally, creating an accurate igarape-themed aquarium would have the bulk of it's population consist of Tetras, Pencifishes, Hatchetfishes, and other characins. What does this tell us about the habitat? Well, for one thing, since the majority of characins feed on items such as insects (terrestrial and aquatic), small crustaceans, and seeds and fruits, we know that the habitat is filled with these items, in the form of allochthonous input. And this usually is a result of the presence overhanging vegetation, decomposing leaves, and various types of riparian plants in these habitats. 

And the presence of various species of catfishes, which, if we look into their dietary preferences, show that many have a preference for wood from fallen branches and submerged tree trunks, organic detritus, worms, biofilm, etc. The rich flooded forest floors have much of this material present in order to support such a diversity! So it's fair to say that, as long as attention is paid to the water chemistry, many species of catfishes are ideal for a botanical-style blackwater aquarium representing this habitat.

And then there are the Knifefishes...

Their presence in the igarape habitats tells us a few things. For one, that the aquatic environment there is a twisted, tangled world of fallen trees, branches, submerged plants, leaves, and lots of places to hide. It tells us that, since a large art of their diet is worms, aquatic insects, and small fishes, the these are productive and rich habitats for these organisms as well. It tells us that these fascinating, cryptic, largely predatory fishes tend to aggregate, like every fish- where their prey items are most easily found.

And of course, the cichlids are present in good numbers in these habitats, exploiting the available food sources and spawning areas to hunker down for long periods during the inundation.

Cichlids, like all of the other fishes present in these habitats, make ample use of the resources available to them. They are present because the physical and environmental conditions work for them. This is a ridiculously simple concept that we as aquarists seem to know well...but I think we can execute better with more accurate information from nature.

In fact, I think that looking into the fish populations of natural habitats is key to understanding how to create a successful stocking plan. Now, granted, you probably aren't going to keep large, predatory knife fishes or catfishes with your tetras- but smaller representatives of their groups are perfect in the correctly-sized aquarium.

And, having a diversity of fish species that reflects the wild population can do...what? Perhaps, yield some insights into their natural behaviors? Feeding preferences? Reproduction? Can we create better representations of the "structural-functional" aspects of their environment in our aquaria?  By understanding where our fishes are found- and more importantly- how- we can potentially unlock many new insights into their captive care. It's a game that's been going on for centuries in the hobby, but if we take newly-avialble data and really look at it with some fresh perspectives...what can we unlock when we follow the fishes?

Until next time...

Stay curious. Stay intrigued. Stay creative. Stay adventurous...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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