Function, form, and the call of "microhabitats" and niches...

One of the most nitrating things about our era of aquarium keeping is that we have access to an enormous amount of information about the wild habitats of our fishes. If you make the effort, you can find scientific research papers on just about any fish, locale, and habitat you can think of. With all of this information available, the sheer number of habitats which you can replicate in an aquarium is mind boggling!

And it's not just habitats, per se- it's little ecological niches within the habitats- known to ecologists as "microhabitats" -defined  as habitats which are small or limited in their extent, and which differ in character from some surrounding more extensive habitat.

These can be both compelling and rewarding to use as an aquarium subject! And, not surprisingly, these may encompass simple materials which we as botanical-method aquarium enthusiasts are quite familiar with! In many natural aquatic habitats, fallen tree branches, twigs, and leaves, form a valuable and important part of the ecosystem. 

The complexity and additional "microhabitats" they create are very useful for protecting baby fishes, breeding Apistogramma, maintaining Poecilocharaxcatfishes, Dicosssus, and other small, shy fishes which are common in these locales. They provide foraging areas, as well as locations to sequester detritus, sediments, and nutrients for the benefit of the surrounding ecosystems.

It would be remarkably easy- and interesting- to replicate these habitats within the confines of the aquarium. The mind-blowing diversity of Nature is comprised of millions of these little "scenes", all of which are the result of various factors coming together.

As aquarists, observing, studying, and understanding the specifics of microhabitats is a fascinating and compelling part of the hobby, because it can give us inspiration to replicate the form and more important- the function-  of them in our tanks!

We spend a lot of time discussing and considering the various components and interactions of water and terrestrial habitats, and I think that if WE haven't made a compelling case, our Nature will!

Consider the "karsts..."

A karst is an area of land made up of limestone. Limestone, also known as chalk or calcium carbonate, is a soft rock that dissolves in water. This process produces geological features like ridges, towers, fissures, sinkholes and other characteristic landforms. Many of the world’s largest caves and underground rivers are located in karstlands.

(Karstic terrain. Image by Jan Nyssen used under CC BY-SA 4.0)

The porous limestone rock holds a lot of groundwater, ponds, and streams, sometimes located underground. And those cool  structures known as cenotes (closed basins)! Yeah, we'll revisit those some other time.

Karsts are characterised by the presence of caves, sink holes, dry valleys and "disappearing" streams. These landscapes are known for their groundwater flow and efficient drainage of surface water through a wide network of subterranean conduits, fractures and caves.

Karst are found throughout the world, including France, China, the Yucatán Peninsula; South America, and parts of the United States.

In typical karstic habitats, the water is very clear, becoming turbid after heavy rains. Flash floods occur several times during the rainy season. In this period the stream width increases, making available habitats to be colonized, called  "temporary stretches".

Are you thinking what I'm thinking? Yeah, these could be interesting aquarium subjects! 

Yeah. And since a bunch of 'em occur in South America, where some of our fave fishes come from...this could be really interesting!

A fascinating neotropical karst landscape is located in the São Francisco River basin, Minas Gerais State, in Brazil. The fish diversity in these waters is significant. One study that I stumbled upon identified 28 species distributed in 3 orders and 9 families in this one locale alone!

The pH values in the South American karst habitats I found studies on range from 6.3 to 8.2, and averaged around 7.2 (slightly alkaline). Water temperatures average around 75 degrees F ( 23.8C), conductivity averages .30mS/cm, and the ORP averages 178 mv. (lower than one might expect, right? In reef keeping, we shoot for around 300 mv, so...) It's thought that the low levels of ORP can be associated with environmental pollution and/or high concentrations of ions, which is consistent in waters with karstic origins.

From an aquarist's perspective, karstic habitats should be pretty easy to replicate in the aquarium, right? Lots of smooth stone and sand, with a scattering of leaves and a few branches. This is one instance where I'd tell you to use plenty of activated carbon or other chemical media, to keep the water more or less clear. I mean, in some locales, as we mentioned previously, it's crystal clear!

Lots of epiphytic algal growth, some broken up leaves, aggregations of rocks...sand...I mean, this is like aquarist paradise! You can pretty much use every trick in the book and still come up with a reasonably faithful biopic representation- functionally aesthetic, no less! And, for some of you, not to have to deal with super acidic water and dark tint could be a real win, huh?


This is the most cursory description of karsts- but I hope it whets your appetite to learn more about them! Dig deeper, and you'll find a remarkable amount of information about them.

And of course, I can't just discuss one interesting habitat without mentioning another, right? 

Among the richest habitats for fishes in streams and rivers are so-called "drop-offs", in which the bottom contour takes a significant plunge and increase in depth. These are often caused by current over time, or even the accumulation of rocks and fallen trees, which "dam up" the stream a bit. (extra- you see this in Rift Lakes in Africa, too...right? Yeah.) 

Fishes are often found in drop offs in significant numbers, because these spots afford depth (which thwarts the hunting efforts those pesky birds), typically slower water movement, numerous "nooks and crannies" in which to forage, hide, or spawn, and a more restive "dining area" for fishes without strong currents. They are typically found near the base of tree roots...From an aquascaping perspective, replicating this aspect of the underwater habitat gives you a lot of cool opportunities.

And of course, these types of habitats are perfect subjects for aquarium representation, aren't they?

If you're saddled with one of those seemingly ridiculously deep tanks, a drop-off could be a perfect subject to replicate. And there are even commercially-made "drop-off" tanks now! Consider how a drop-off style encompasses a couple of different possible niches in the aquarium as it does in Nature!

Overhanging trees and other forms of vegetation are common in jungle/forest areas, as we've discussed many times. Fishes will tend to congregate under these plants for the dimmer lighting, "thermal protection", and food (insects and fruits/seeds) that fall off the trees and shrubs into the water. (allochthonous input- we've talked about that before a few times here!) And of course, if you're talking about a "leaf litter" or botanically-influenced aquascape, a rather dimly-lit, shallow tank could work out well.

And of course, in the areas prone to seasonal inundation, you'll often see trees and shrubs partially submerged, or with their branch or root structures projecting into the water. Imagine replicating THIS look in an aquarium. Contemplate the behavioral aspects in your fishes that such a feature will foster!

Lots of leaves, small pieces of wood, and seed pods on the substrtae- doing what they do- breaking down-would complete a cool look. For a cool overall scene, you could introduce some riparian plants to simulate the bank as well. A rich habitat with a LOT of opportunities for the creative 'scaper!

Why not create an analogous stream/river feature that is known as an "undercut?" Pretty much the perfecthiding spot for fishes in a stream or river, and undercuts occur where the currents have cut a little cave-like hole in the rock or substrate material near the shore.

Not only does this feature provide protection from birds and other above-water predators, it gives fishes "express access" to deeper water for feeding and escaping in-water predators!

Trees growing nearby add to the attractiveness of an undercut for a fish (for reasons we just talked about), so subdued lighting would be cool here. You can build up a significant undercut with lots of substrate, rocks, and some wood. Sure, you'd have some reduced water capacity, but the effect could be really cool.

Yeah, I could go on and on with all sorts of ideas about how to recreate all sorts of microhabitats in the aquarium- because there are a seemingly limitless number of them to explore and replicate! 

There is a reason why all of these unique environments are successful, and why life exists- and indeed- thrives- in them. And there are reasons why we're starting to see incredible results when replicating some of the functional aspects of these environments in a more faithful manner than may have been attempted before.

And we have all of the "tools" that we need to do this:

Patience. A long-term view. Information. Observation. Understanding.  

You've got this.

Stay creative. Stay enthusiastic. Stay observant. Stay patient. Stay excited...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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