February 06, 2021

Filled with inspiration: The many wonders of stream habitats.

As you know, I have a VERY healthy obsession with leaf litter beds in the wild and in my aquariums. The way that leaves and other materials accumulate in watercourses such as streams has a profound influence on the the lives of our fishes.

Leaf litter beds form in what stream ecologists call "meanders", which are stream structures that form when moving water in a stream erodes the outer banks and widens its "valley", and the inner part of the river has less energy and deposits silt- or in our instance, leaves.

There is a whole, fascinating science to river and stream structure, and with so many implications for understanding how these structures and mechanisms affect fish population, occurrence, behavior, and ecology, it's well worth studying for aquarium interpretation!

Did you get that part where I mentioned that the lower-energy parts of the water courses tend to accumulate leaves and sediments and stuff?

It's logical, right? And it's also interesting, because, as we know, fishes and their food items tend to aggregate in these areas, and embracing the "theme" of a litter/botanical bed or even wood placement, in the context of a stream structure in the aquarium is kind of cool!

In Nature, the rain and winds also effect the depth and flow rates of many of the waters in this region, with the associated impacts mentioned above, as well as their influence on stream structures, like submerged logs, sandbars, rocks, etc.

Stuff gets redistributed constantly.

Is there an aquarium "analog" for these processes?

Sure!

We might move a few things around now and again during maintenance, or perhaps current or the fishes themselves act to redistribute and aggregate botanicals and leaves in different spots in our aquairums.

And how we structure the more "permanent" hardscape features in our tanks has a profound influence on how botanical materials can aggregate.

So, rather than covering the whole bottom of your tank with leaves, would it be cool to create some sort of hardscape structure- with driftwood, etc., to retain or keep these items in one place..to create a "framework" for a long-term, organized, specifically-placed litter bed.

You could build upon, structure, and replace leaves and botanicals in this "framework"- like, indefinitely...sort of like what happens in the "meanders in streams!"

How would fishes react when presented with a deep litter bed in part of the aquarium; would they prefer to reside there? Or would they simply forage there and stay in the more open areas of the aquarium? Would the spawn there?

Probably some fry would seek shelter there, right?

Streams typically feature two interesting biotopes that we haven't really discussed in much detail here, and both of which are quite profoundly impacted by the seasonal rains: Pools, with slower current and a substrate covered mainly by deposits of leaf litter, detritus and driftwood; and "rifﬂes" (defined as shallow sections of a stream with rapid current and a surface broken by gravel, rubble or boulders), with a moderately-fast-ﬂowing current and mostly sandy bottom with tree roots, driftwood pieces, and small rocks and pebbles. (ohh...home to Darter Characins!)

I'm thinking cool niche biotope aquarium possibilities here...

The "riffles" are considerably more significant in the wet season, when the obvious impact of higher water volumes are present. In the Amazon, for example, you'll find an unexpected abundance of some species familiar to us as hobbyists in these "riffles." Species like Pyrrhulina brevis, Hyphessobrycon melazonatus, and Hemigrammus of various forms, and even some Nanostimus, and the killie Rivulus compressus!

Some researchers have postulated that the higher presence of nocturnal predators in the pools adjacent to the more active riffles might increase the number of species that seek refuge in the riffles to avoid them! And Rivulus, which usually live in more intermittent pools along the stream edges, outside the main stream channels, are normally found at night in these rifﬂes!

So, protection from predators- survival- is a powerful motivation for fishes to seek out these different habitats. Now, granted, in the aquarium we are almost guaranteed NOT to keep predators and prey in the same tank (at least, not for long-term display purposes!), but is there not something to be gained by replicating the environments that some of our aquarium fishes come from?

Reduction of stress. Indeed, survival. That's pretty important in the wild...so I'd imagine it's equally as important in the aquarium. And of course, in the aquarium, we're all about fostering of natural behaviors...Even if they are not "necessary" for survival. I can't hope but wonder if providing some of these more specific environmental conditions (in concert with stuff like water chemistry and the presence of stuff like leaves, wood, etc.) could facilitate greater possibilities for spawning, long-term health, and greater lifespan?

Stream and river bottom composition is affected by things like regional weather, current, geology, the surrounding dry lands, and a host of other factors- all of which could make planning your next aquarium even more interesting if you take them into consideration!

If we focus on streams, it's important to note that the volume of water entering the stream, and the depth of the channels it carves out, helps in part determine the amount and size of sediment particles that can be carried along, and thus comprise the substrate.

And of course, the composition of bottom materials and the depth of the channel are always changing in response to the flow in a given stream, affecting the composition and ecology in many ways.

Permanent streams will often have different volume and material composition (usually finely-packed sands and gravels, with lots of smooth stones) than more intermittent streams, which are the result of inundation caused by rain, etc.

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). The latter two stream types are typically more affected by leaves, botanical debris, branches, and other materials.

In the Amazon region (you knew I was sort of headed back that way, right?), it sort of works both ways, with the rivers influencing the surrounding land...and then the land "giving" some of the materials back to the rivers...the extensive lowland areas bordering the river and its tributaries, known as varzeas (“floodplains”), are subject to annual flooding, which helps foster enrichment of the aquatic environment.

Although many streams derive their food base from leaves and organic matter, there is a lot of other material present that contributes to its structure. Think along those lines when scheming your next aquarium. Ask yourself what factors would contribute to the bottom composition of the area you're taking inspiration from.

You'll see a variety of bottom compositions in Amazonian and other streams, ranging from the aforementioned leaves and detritus in stream margins, to sand and silt over "cobbles", to boulders covered in algae, to fine patch gravels, and even just silt.

You might even say that rivers and streams act like nature's "sediment sorting machines", as they move debris, geologic materials, and botanicals along their courses. And along the way, varying ecological communities are assembled, with all sorts of different fishes being attracted to different niches.

In streams, studies indicate that an increase in species "richness" is positively related to the habitat complexity and shelter availability as well as current velocity and stream size, and that substrate, depth and current speed are among the most important physical features in many bodies of water, which contribute to the formation of numerous "microhabitats", all with fascinating ecology, environmental parameters, and fish population diversity.

Stuff we've barely tapped into in the aquarium world yet!

The implications of this information for aquarists are profound and fascinating, and understanding, interpreting, and applying some of these numbers and concepts can potentially lead to some fascinating breakthroughs in aquarium work.

However, we have to "get out of our own way", first.

We're talking about taking the lead from Nature- looking at it as it IS- and about using this stuff to create aesthetically compelling, dynamic, and physically functional aquariums. There is always the danger of going toofar, and falling into that cliche of closed-minded superficial replication that is, in my opinion, consuming the aquascaping and biotope aquarium world, so use the information you find with a bit of interpretation...but make use of it nonetheless.

The "look" and the "function"- working hand in hand to create a replication of Nature far more authentic than what we've done in the past in the hobby. And what is required to execute this?

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

You've got this.

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

And Stay Wet.

Scott Fellman

Tannin Aquatics