June 28, 2018

Chasing the food...A most compelling aspect of our blackwater habitats and the aquariums which replicate them

With this whole blackwater thing really starting to explode worldwide, it's fun to look at some of the different habitats that we can draw inspiration from. Geographically, few areas of the world make one think of "blackwater" more than South America- specifically, The Amazonian region.

And why not, right?

This is an area that spans tens of thousands of square kilometers and has an enormous variety of what environmental scientists call "macrohabittas." Many of these which are better known to aquarists are comprised of what we call "whitewater", which is typically pH neutral, rich in nutrients and suspended matter (like silt and such). These are commonly associated with the so-called varzea- seasonally flooded forests inundated by whitewater rivers.

And of course, the habitats which fascinate us the most are the macrohabitats of the blackwater habitats associated with the igapo flooded forests- waters extraordinarily rich in humic substances, relatively poor in nutrients, and quite acidic!

And, as we've discussed previously, the fish population and diversity in these igapo regions, long thought to be somewhat "impoverished", is actually very diverse and significant. Studies have revealed that many fishes are found in the submerged litter bank of these regions, forming dense local populations which are specialized and live on the allochthonous inputs (defined as material that imported into an ecosystem from outside of it) from the inundated forest floors.

The fishes have adapted to live in an environment with varying leaf and wood density, and seasonal variations in depth.

And the food production of these habitats!

The seasonal flooding brings fishes into contact with a greater abundance and diversity of allochthonous food resources, especially within forested watersheds, and this is significant to their life cycle.

With regards to the types of fishes we find in these habitats, scientists have found repeatedly that the majority seem to be characins, followed by Loricariids, cichlids, and "everything else."

Let's just touch a bit more on the allochthonous inputs that our fishes utilize in the wild, and can no doubt benefit from In the aquarium, as well.

One of the important food resources in natural aquatic systems are what are known as macrophytes- aquatic plants which grow in and around the water, emerged, submerged, floating, etc.

Not only do macrophytes contribute to the physical structure and spatial organization of the water bodies they inhabit, they are primary contributors to the overall biological stability of the habitat, conditioning the physical parameters of the water. Of course, anyone who keeps a planted aquarium could attest to that, right?

One of the interesting things about macrophytes is that, although there are a lot of fishes which feed directly upon them, the plants themselves are perhaps most valuable as a microhabitat for algae, zooplankton, and other organisms upon which fishes feed on. Small aquatic crustaceans seek out the shelter of plants for both the food resources they provide (i.e.; zooplankton, diatoms) and for protection from predators (yeah, the fishes!). And leaf litter, botanical materials, etc. serve as perfect shelter for these macrophytes in which to grow and multiply.

Perhaps most interesting to us blackwater/botanical-style aquarium people are epiphytes. These are organisms which grow on the surface of plants or other substrates and derive their nutrients from the surrounding environment. They are important in the nutrient cycling and uptake in both nature and the aquarium, adding to the biodiversity, and serving as an important food source for many species of fishes.

In the case of our aquatic habitats, like streams, ponds, and inundated forests, epiphytes are abundant, and many fishes will spend large amounts of time foraging the biocover on tree trunks, branches, leaves, and other botanical materials. Although most animals use leaves and tree branches for shelter and not directly as a food item, grazing on this epiphytic growth is very important. Some organisms, such as nematodes and chironomids ("Bloodworms!") will dig into the leaf structures and feed on the tissues themselves, as well as the fungi and bacteria found in and among them. These organisms, in turn, become part of the diet for many fishes.

And the resulting detritus produced by the "processed" and decomposing pant matter is considered by many aquatic ecologists to be an extremely significant food source for many fishes, especially in areas such as Amazonia and Southeast Asia, where the detritus is considered an essential factor in the food webs of these habitats. And of course, if you observe the behavior of many of your fishes in the aquarium, such as characins, cyprinids, Loricarids, and others, you'll see that in between feedings, they'll spend an awful lot of time picking at "stuff" on the bottom of the tank. In a botanical style aquarium, this is a pretty common occurrence, and I believe an important benefit of this type of system.

I am of the opinion that a botanical-style aquarium, complete with its decomposing leaves and seed pods, can serve as a sort of "buffet" for many fishes- even those who's primary food sources are known to be things like insects and worms and such. Detritus and the organisms within it can provide an excellent supplemental food source for our fishes!

The dynamic of input and utilization of materials from the surrounding forest is fascinating and profound for those of us who wish to mimic these habitats in our aquariums...And it actually plays right into our very human behavioral patterns, too!

What do I mean? Read on...

During the rainy season, overflowing streams flood the rainforest floor, accumulating materials which the fish communities utilize for food and shelter. And materials which fall from the surrounding trees and banks are major contributors to the productivity of this ecosystem. As the waters recede somewhat, temporary streams flow through these areas.

It's well known that in many habitats, like inundated forests, etc., fishes will adjust their feeding strategies to utilize the available food sources at different times of the year, such as the "dry season", etc. And it's also known that many fish fry feed actively on bacteria and fungi in these habitats...so I suggest (one again) that a blackwater/botanical-style aquarium could be an excellent sort of "nursery" for many fish species!

And then there are those insects...

Insects and their larvae, from both the the aquatic habitat and the surrounding terrestrial habitats, are an important part of our fishes' diets.

I'd like to see much more experimentation with foods like ants, fruit flies, and other winged insects. Of course, I can hear the protests already: "Not in MY house, Fellman!" I get it. I mean, who wants a plague of winged insects getting loose in their suburban home because of some aquarium feeding experiment gone awry, right?

That being said, I would encourage some experimentation with ants and the already fairly common wingless fruit flies. Can you imagine one day recommending an "Ant Farm" as a piece of essential aquarium food culturing equipment?

Why not right?

Indeed, the whole process of these external inputs can be-should be- replicated in our botanical-style, blackwater aquariums.

As more materials fall from the trees and surrounding dry areas, the greater the abundance of fishes and other aquatic animas which utilize them is found. And materials will continue to fall into the water and accumulate throughout the period of inundation, maintaining the richness of the habitat as others decompose or are acted on by the organisms residing in the water.

Not unlike an aquarium, right?

It makes me think that our process of adding and replacing new materials to our botanical-style blackwater aquariums is a very good representation of what occurs in these habitats.

I firmly believe that the idea of embracing the construction (or nurturing) of a "food web" within our aquariums goes hand-in-hand with the concept of the botanical-style, blackwater (and brackish!) aquarium. With the abundance of leaves and other botanical materials to "fuel" the fungal and microbial growth, and the diligent husbandry and intellectual curiosity of the typical "tinter", the practical execution of such a concept is not too difficult to create.

We are truly positioned well to explore and further develop the concept of a "food web" in our own systems, and the potential benefits are enticing!

Appetizing?

Stay curious. Stay excited. Stay creative...

And Stay Wet.

Scott Fellman

Tannin Aquatics