Natural Habitats we should replicate more in aquariums

From time to time, I like to think about creating aquariums based on some of those seldom-replicated habitats and ecological niches. I find that there is something oddly compelling about recreating the function and form of some rather exotic habitats.

I wonder why they haven't been replicated more in the past, and then I realize it's likely because we don't really understand all that much about how they function. Perhaps, we haven't done much with some of these unusual niches for the most absurd of all reasons: Because no one else has tried it before!

It's time to be brave, and try a few of these. I'll give you a little cover and tell you that I've tried various versions of each one of these over the years; much more needs to be done with them, however. 

What insights could we gain by learning more about them? Let's look at a few of my personal faves, and give some thought to recreating them in our aquariums...

African Temporal Pools

Africa is a veritable treasure trove of amazing ecological niches for aquarists to study and replicate in the aquarium in form and function. Vernal or temporal pools are typically found in areas comprised of various soil types that contain clays, sediments and silts. They can develop into what geologists call "hydric soils", which  are defined as, “...a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part.”

Well, that's interesting! 

A unique part of the vernal pools is what is an essentially impermeable layer of substrate called "clay pan."  These substrates are hugely important to the formation of these habitats, as the clay soils bind so closely together that they become impermeable to water.  Thus, when it rains, the water percolates until it reaches the "claypan" and just sits there, filling up with decaying plant material, loose soils, and water.

So, yeah- the substrate is of critical importance to the aquatic life forms which reside in these pools! Let's talk killies for a second!  One study of the much-loved African genus Nothobranchius indicated that the soils are "the primary drivers of habitat suitability" for these fish, and that the eggs can only survive the embryonic period and develop in specific soil types containing alkaline clay minerals, known as "smectites", which create the proper soil conditions for this in desiccated pool substrates.

The resulting "mud-rich" substrate in these pools has a low degree of permeability, which enables water to remain in a given vernal pool even after the surrounding water table may have receded! And, of course, a lot of decaying materials, like plant parts and leaf litter is present in the water, which would impact the pH and other characteristics of the aquatic habitat.

Indeed, many ephemeral pools have high levels of dissolved organic carbon (such as humic acids) derived from decomposing plants that turn the water a clear brown color.

Why do fishes even live in these rather harsh environments?

I mean, they're typically small, isolated, and prone to weather disturbances and extreme temperatures. There ARE some interesting advantages that these habitats offer. First, they have significant food resources, because they're a favorable environment for many small invertebrates and insects. In addition, they are home to fewer spaces, reducing competitive pressures on the fish. (Most ephemeral pools are populated by a single species, or perhaps two or three, utilizing different food resources within the pool)

Interestingly, it is known by ecologists that the water in ephemeral pools may stay alkaline despite all of the leaves and other botanical materials present, because of the buffering capacity of the alkaline clay present in the sediments!

And, to literally "cap it off"- if this impermeable layer were not present, the vernal pools would desiccate too rapidly to permit the critical early phases of embryonic development of the Nothobranchius eggs to occur. Yes, these fishes are tied intimately to their environment.

(Image by Andrew Bogott, used under CC BY-S.A. 4.0)

in the dry part of  the range of the genus Nothobranchius in southwestern Mozambique, many pools inhabited by the well-known killies,  N. furzeri and N. orthonotus are usually isolated from more permanent bodies of water, and are filled exclusively by rainwater during periods of high precipitation. Some of these pools, however, may be occasionally connected, as they are essentially depressions in the dry savannah, in which water drained from these larger bodies of water, accumulates.

These pools and their cycles directly impact the life cycle and reproductive strategies of the annual fishes which reside in them. Temporary pool fish have made incredible adaptations to deal with their fluctuating environment. It's little wonder why many of these fishes are incredibly easy to keep in aquariums!

The fascinating concept of embryonic diapause ( a form of prolonged, yet reversible developmental arrest) is well-known to scientists and lovers of annual killies. The occurrence and length of time of diapause varies from species to species, yet is considered by scientists to be an evolutionary adaptation and ecological trait in various populations of Nothobranchius, tied directly into the characteristics of the ephemeral habitats in which these fish reside!

Diapause assures species survival by enabling the annual life cycle of these fish to be completed, and can even be affected by the presence of adult fishes in the habitat (not a good idea to hatch if potential predators are around, right?)- a fascinating adaptation! Since the embryonic phase of most Nothobranchius is a relatively long period of their lives- and in some species- the longest phase of their life, factors which impact embryonic development are extremely important. 

Okay, my head is about to explode here with this really interesting stuff! 

(Image by Kils- used under CC BY-S.A. 3.0)

So, we tend to use peat as the substrate and incubation media for annual killifishes. It's worked great for many decades in this capacity. I can't help but wonder if using hydric soils; clay-rich materials- in order to more realistically replicate the function of the substrates found in the wild African habitats-could yield better, more consistent egg development in annual killies?

In general, sediments and mud, in conjunction with botanical materials, are things that we as hobbyists should do more experimentation with.

I could imagine an aquarium designed simply to replicate a temporal pool, mud hole, or flooded field. A substrate only tank would be incredibly different...and I can only imagine what discoveries could be made by recreating the function and look of such a habitat in the aquarium.


Peat Swamp Forests

The island of Borneo is widely known as one of the most biodiverse ecosystems on earth, and the peat swamp forests there cover around 12% of the land in Southeast Asia! Peat swamp forests are a form of tropical forest in which very saturated soils (called "histosols" by geologists) inhibit the decomposition of organic materials, such as leaves and other parts of trees and forest vegetation, which leads to the formation over time of peat.

In areas with poor drainage, peat can accumulate over long periods of time until it rises above normal groundwater levels, which creates raised bogs, known to ecologists as "ombrogenous" bogs, which are fed only by rain, and thus have their own water table. The peat retains water via capillary action. These bogs can be as much as 60 feet (20 meters) deep(!), and are largely deficient in nutrients because of the lack of input of mineral input. The leaching of organic compounds from the peat causes the water contained in these bogs to be extremely acidic (like pH4 or lower!).

These "omborgoenous" peat swamps can develop in in areas between rivers in locales with year-round rainfall, as well. They're fascinating structures, home to an enormous diversity of life. Here's where it gets interesting to us fish geeks:

Studies have shown that approximately 219 species of fishes have been found in peat swamps, with approximately 80 of these species restricted to this habitat alone! And 31 are what are known as "point endemic" species, found only in single locations!

That's a LOT of species in a very unique habitat, huh?

 (image by Marcel Silvius)

Some scientists suggest that the conditions in peat swamps have favored the evolution of smaller, specialized fish species, and that each area of peat swamp could support its own  group of endemic species. This is interesting and important...Some species (17 have been identified at the moment) from these habitats are classified as vulnerable, endangered, or critically endangered.

Species from the genera Sphaerichthys, Desmopuntius, Rasbora, Betta, and Channa are well-represented in these habitats.

Average water depth in these swamp habitats ranges from about 1/2" to as much as 3 feet (approx. 0.1 meters to 0.9 meters).  Researchers have found that these peat swamp fish communities are typically more species rich in habitats which offered higher levels of dissolved oxygen, interesting because we tend to think of swamp fish as being found typically in low oxygen environments, right?

That being said, there are plenty of fishes which have evolved to thrive in these habitats. For example, Betta hendra, one of the betta species, is only known to be found in the Sebangau forest! These are also specially adapted for life in the peat-swamp environment, with its lower dissolved oxygen levels. According to Fish Base, it's found in Found in, "...peat swamps with depth of about 5 to 50 cm and with no water current. The water was shaded by trees and bushes. Collected among the aquatic and marsh plants..."

(A great pic of B. hendra by our friend, Sumer TIwari)

Another gem from my research about dissolved oxygen levels and their impact on fish populations:

"Forest pools and canals in these regions have consistently lower dissolved oxygen levels the rivers and streams in the region do. This is probably due to the inherent nature ofthe aquatic habitat in peat swamp forests, where DO levels are kept low due to the high amount of tannins in the water (from the high organic matter content of the peat), with the accumulation of decaying organic matter depleting DO levels.

Additionally, there is low or no water flow (especially in the pools) which further ensure low levels of DO regardless of the lower surface temperatures of forest water bodies(Yule & Gomez 2009). Low concentrations of DO can make water uninhabitable for certain fish species, therefore the forest is likely to be a more challenging environment for fish survival."

Did you see the part about the tannins keeping dissolved oxygen levels lower? That's the first time I've heard that correlation made. Although, the next sentence clarified it for me, when it touched on the high level of organic matter depleting dissolved oxygen levels. So, my thinking is that the tannin is the result of the organic matter, but the organic matter itself is responsible for the lower oxygen levels.

This makes perfect sense, right?

We all know by now that too much botanical material added to the water in your aquarium in a short time period can result in depleted oxygen levels, leaving fishes gasping at the surface! If there is one "common botanical-style aquarium disaster trigger", that would be it. See- that happens in Nature happens in our aquariums. You can push it, but you can't hide from the consequences of trying to beat Nature's rules!

Now, many of us have mixed feelings about utilizing peat in our aquariums; however, there ARE some sources of sustainably-harvested peat available, but you'll have to do your homework to find them. We've covered this conundrum a couple of years back right here in "The Tint."

Are there alternatives? 

Well, sure. I think so.


In peat swamps, the peat layers may be well in excess of  3 feet (1m) deep. The floodplain forests are found along rivers, streams, coasts, and lakes. The seasonal flooding inundating the forests for short periods leads to an influx of sediment and mineral enrichment during high water periods. 

These soils are best replicated by using "non-traditional" substrates, like...coconut-based materials, finely-crushed botanicals, mud, sediments, etc...

(If you're thinking that we should come out with a "NatureBase" substrate inspired by this habitat, your correct!I've already formulated a version, and have been testing it for some time. We'll definitely release it as a "limited release" substrate in the coming months! 

There are some characteristics of these soils which will make them challenging in aquariums. For one thing, the physical characteristics of these materials will make them "behave differently" in water than traditional sands and other aquarium substrates. Peat, in its natural state, contains excessive amounts of water and is not exactly "sturdy" like sand or gravel because of its high permeability and has very low shear strength. And of course, it has a really low pH.

If we're trying to replicate the habitat as faithfully as possible, we'd want to use reverse osmosis/deionized water, or water with minimal carbonate hardness, and a soil with properties similar to peat. This could be challenging to manage for many hobbyists, because of the resulting pH. Not impossible- simply challenging.

We're going to have much, MUCH more to talk about with this unique habitat in coming months...stay tuned!

Flooded Pantanal Grassland

Thanks to our friend, Tai Strietman, we've seen some really interesting and inspiring images of this unique habitat. 

The Pantanal (derived from the Portuguese word "pantano"- meaning "swamp", "wetland", or "marsh") is the largest wetlands region Earth. Full stop. Primarily located within the Brazilian state of Mato Grosso do Sul, it also extends into the state of Mato Grosso, and the nations of Paraguay and Boliva as well! We're talking about region estimated to be as large as 75,00 square miles/195,000 square kilometers!  

It's freakin' huge! 

Essentially a large depression in the earth's crust, the Pantanal constitutes a huge river delta, into which a number of rivers converge, depositing sediments and other biological materials. Now of course, with a habitat this large, there are multiple ecosystems contained in it- as many as 12 have been defined by scientists! 

(Image by Alicia Yo- used under CC BY-SA 3.0)

Now, our main focus is, of course, fishes- and the Pantanal offers plenty of places for fishes to reside in! The cool thing about the Pantanal is that as much as 80% of it is floodplains submerged during the rainy seasons (in which up to 59inches/1,500mm of rainfall have been recorded! That corresponds to water depths which can fluctuate up to 15'/5 meters in some areas!), and is home to an astonishing diversity of fishes and aquatic plants!

With it's enormous expanse of shallow, slowly-flowing water (velocities of no more than 4"/10cm per second are typical), dense vegetation-terrestrial and aquatic- tends to be the norm here. 

The water itself tends to be turbid, and perhaps even a bit anoxic at times. And, interestingly, the highest levels of pH and dissolved oxygen in these habitats tend to occur when the water decreases and plant growth is stimulated. Curiously, however, scientists are not 100% certain if this is because of the plants going crazy with photosynthesis, or mixing of the water column due to influx of water. 

Macrophytes (aquatic plants that grow in or near water and are either emergent, submergent, or floating) supply shelter, food resources and cover for the resident fishes. Still other fishes consume the aquatic insects and microorganisms/biofilms that are recruited in this habitat. Most are well-adapted to the relatively oxygen-poor waters of this vast flood plain.

So, it goes without saying that this is a remarkably complex habitat, with multiple options for replication in the aquarium! I think your first decision is to decide what, if any aquatic plants you'd use. Aquatic plants found in Pantanal habitats include such popular aquarium species as Polygonum, Salviania, Pistia, Ludwigia, and more. You could also incorporate some marginal plants, like Acorus, Papyrus, and other "sedges", to represent the flooded or emergent terrestrial plant component found in these habitats.

Personally, for substrate, I'd utilize a fine sand, perhaps with a powdered form of aquatic plant substrates mixed in. On the surface, you'd certainly want to incorporate some leaves. They're ubiquitous in this habitat. Specifically, leaves like Jackfruit, Guava, and Texas Live Oak leaf litter would work well to represent the appearance and function of the leaf litter component.

In addition to leaves, you could certainly incorporate some other botanical materials, like seed pods. If it were me, I'd be inclined to use a scattering of smaller seed pods, like Dregea, Mokha, and Parviflora - admittedly, none of which are "geographically correct" and actually found in this habitat- all of which replicate the look of the materials found in it, however!

(that whole "Generic Tropical" concept I rant on and on about...)

And of course, with all of that vegetation, you're bound to find some roots, branches, and twigs...So what better way to represent this than with a group of oak twigs scattered about the substrate. Our recommendation, of course, is our "Twenty Twigs" product, which gives you a nice little variety of twigs to fill in some details! You could go with the "regular" or "Large" size, depending upon your preferences.

How would you 'scape your Pantanal tank? 

This habitat is just FILLED with possibilities for replication! You could represent a nice, flat field, or get a little more daring, and do a sort of "shoreline" feature, with sloping substrate, terrestrial, and aquatic vegetation mixed together.

With so few representations of this amazing habitat in the natural aquarium hobby, and see many opportunities to express it with botanicals, it tells me that not only is The Pantanal simply ripe for replication- it's a perfect "ground-floor" opportunity for studying, learning, discovering, and creating evolutions and breakthroughs in the hobby!

I could go on and on and on, but these are a few ecological niches that I think we should do more work with in our aquariums.

The idea of turning to Nature for inspiration is as old as aquarium keeping itself; however, in recent years, we seem to have moved a bit away from that, drawing more inspiration from other aquarist's work. Again, this is wonderful, and a great thing- symbolic of the interconnected global hobby we're in. However, with so much emphasis on replicating the fine work of other hobbyists, it's nice to gain a fresh perspective from Nature one in a while, incorporating it into our "toolbox" of ideas- in our own way, to create something that we enjoy-something that is truly unique, and which gives us a real "slice of the bottom" as well.

Stay creative. Stay curious. Stay innovative. Stay bold...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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