March 15, 2021

From the depths of our imagination to the shallows of streams...

You're likely aware of the fact that we're crazy about small, shallow bodies of water, right? I mean, almost every fish geek is like "genetically programmed" to find virtually any random body of water irresistible!

Especially little rivulets, pools, creeks, and forest streams. The kinds which have an accumulation of leaves and botanical materials on the bottom. Darker water, submerged branches- all of that stuff...

You know, the kind where you'll find fishes!

Happily, such habitats exist all over the world, leaving us no shortage of inspiring places to attempt to replicate. Like, everywhere you look!

In Africa for example, many of these little streams and pools are home to some of my fave fishes, killifish! Of particular interest are the fishes of the genus Epiplatys. These fishes are outstanding at hiding and are quite adept at it in these little bodies of water, with their tangles of roots and submerged vegetation.

As mentioned above, many of these little jungle streams are really shallow, cutting gently through accumulations of leaves and forest debris. Many are seasonal. The great killie documenter/collector, Col. Jorgen Scheel, precisely described the water conditions found in their habitat as "...rather hot, shallow, usually stagnant & probably soft & acid."

Ah-ah! We know this territory pretty well, right?

I think we do...and understanding this type of habitat has lots of implications for creating very cool biotope-inspired aquariums.

And why not make 'em for killifish?

So, for the most part, these fishes are often found in very shallow jungle streams. How shallow? Well, reports I've seen have stated that they're as shallow as 2 inches (5.08cm). That's really shallow. Like, seriously shallow! And, quite frankly, I'd call that more of a "rivulet" than a stream!

"Virtually still, with a barely perceptible current..." was one description. That kind of makes my case. Like, what you'd see when a small stream overflows it's banks and creates a smaller body of water.

What does that mean for those of us who keep small aquariums?

Well, it gives us some inspiration, huh? Ideas for aquariums that attempt to replicate and study these compelling shallow environments...

An important consideration when contemplating such a replication in our tanks is to consider just how these little forests streams form. Typically, they are either a small tributary of a larger stream, with the path carved out by rain or erosion over time. In other situations, they may simply be the result of an overflowing tributary during the rainy season, and as the waters recede later in the year, they evolve into smaller streams meandering through vegetation.

Those little streams fascinate me.

These interesting little tributaries are usually shaded by trees at the margins, and often cut for many kilometers through dense rain forest. The bottoms of these tributaries- typically former forest floors- are often covered with seed pods, twigs, leaves, and other botanical materials from the vegetation above and surrounding them. Often, the water will pool into even smaller bodies of water.

In this world of decomposing leaves, submerged logs, twigs, and seed pods, there is a surprising diversity of life forms which call this milieu home. And each one of these organisms has managed to eke out an existence and thrive.

So-called "ephemeral" streams, typically occur only immediately after rain events (which means they usually don't have fish in them unless they are washed into them from more permanent watercourses).

Now, I don't expect you to set up a tank with a water level that's 2 inches deep..And, although it would be pretty cool to do that, for more of us, perhaps a 3.5"-4" (8.89-10.16cm) of depth is something that can work? Yeah. Totally doable. There are some pretty small commercial aquariums that aren't much deeper than 8" (20.32cm), and you could adapt other containers for this purpose, right?

We could do this with some of the very interesting South American or Asian habitats, too...Shallow tanks, deep leaf litter, and even some botanicals for good measure.

Replicating these unique habitats creates functionally amazing aquariums, too! These little bodies of water are very productive...

One of the more fascinating scientific observations I stumbled upon in recent years concerns the productivity (in terms of food inputs) of smaller Amazonian streams. It's long been known by science that the primary production of food in these streams has been our friend, allochthonous input- you know, leaves, wood, fruits, blossoms, etc. from the surrounding forests.

And, although there is a lot of "stuff" in these streams, biologists traditionally classified these habitats as "low in biomass." However, recent studies of the microfaunal diversity of these streams (Walker and Feriera), it was found that the stream fauna was aggregated in submerged litter and "may reach considerable densities..."

This observation suggested that the animal community within the submerged leaf litter banks was found in greater abundances- and was of greater importance- to the productivity of these waters than previously believed.

In other words, a lot of life and food happens in submerged leaf litter beds! They provide both food and shelter- two primary factors affecting population density among fishes.

If we carry this out to its logical aquarium interpretation, it becomes more intriguing to contemplate an aquarium with the "hardscape" (for want of a better word) consisting essentially of leaves!

Yeah, you've seen this before here.

How about a long, low aquarium, like the ADA "60F", which has dimensions of 24"x12"x7" (60x30x18cm)? You would only fill this tank to a depth of around 5 inches ( 12.7cm) at the most. You'd use a lot of leaves to cover the bottom. We've done that a few times with great success.

in streams, the primary producers of the food webs that attract our fishes are algae and diatoms, which are typically found on rocks and wood wherever light and nutrients create optimum conditions for their growth. Organic material that enters streams via leaf fall is acted upon by fungi and small organisms, which help break it down.

It is probably no surprise, then, that bacteria (especially in biofilms!) and fungi are the initial consumers of the organic materials that accumulate on the bottom. Like, the stuff many of us loathe. These, in turn, are extremely vital to fishes as a food source.

Hence, one of the things I love so much about utilizing a leaf litter bed as a big part of your substrate composition in an aquarium! Of course, we talk about that all the time, right?

We do. And we'll continue to look into more ways to replicate these little shallow bodies of water in our aquariums, because the streams of the world are just a starting point for us to explore in our quest to create more realistic, functionally aesthetic aquariums that will provide enjoyment, education, and inspiration for others.

Stay inspired. Stay excited. Stay creative. Stay observant. Stay resourceful...

And Stay Wet.

Scott Fellman

Tannin Aquatics