February 01, 2021

The abundance.

As you know, I've devoted quite a large amount of time to researching the idea that botanical-style aquariums can provide supplemental nutrition for the fishes which reside in them.

And, yeah- here's yet ANOTHER discussion on this topic!

I think this is hugely important...so much that I'm writing about the subject constantly, huh? However, this time, I"m bringing along some data I gleaned from studies done on fishes from some of the wild habitats we love so much as ammunition!

The "ammunition" is really more of an argument for my hypothesis that our botanical-style aquariums produce meaningful amounts of supplemental foods of similar type and in a variety like that found in some of the natural habitats of our fishes.

It starts with looking at one of my favorite "factoids" that you can find about or fishes in scientific papers- the "gut content analysis", which essentially tells you what the fishes have been eating in the locality where they were collected. These little GCA's give us a ton of usable information for hobby purposes, IMHO! Not only do we learn what the fishes consume; it also gives us some insight about the ecology of the ecosystems where they are found...Lots of good stuff!

Here's an interesting volumetric composition by percent of some of the foods which were found in gut-content analysis of a Rivulus killifish species from a flooded South American forest floor: Vascular Plant Detritus: 45%, Green Algae: 18%, Detritus: 12%, Filamentous Blue/Green Algae: 8%, Diatoms: 6%, Bacterial aggregates: 3%

And a very interesting analysis from a Hyphessobrycon species: Detritus: 21%, Small Amphipods: 18%, Sediment: 15%, Filamentous Algae: 11%, Ostracods: 7%, Benthic Diatoms: 6%, Copepods, 6%, Chirononomid Larvae: 6%, Isopods: 3%, Undifferentiated insects: 3%, Nematodes: 2%, Bacterial aggregates: 2%

Now, sure, there are items like aquatic crustaceans and insects which comprise part of the diets of these fishes, but what's even more interesting to me is the percentage of detritus which makes up part of the gut contents of these fishes!

Yeah, our old friend, detritus.

Go figure.

I mean, it makes perfect sense, really...A lot of what's available for fishes throughout the lean and the abundant times of the year is detritus, made up of "assorted organic materials."

Let's trot out that definition I love so much one more time:

"detritus is dead particulate organic matter. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose or remineralize the material." (Source: The Aquarium Wiki)

Think about it...A mix of stuff you'd find just about anywhere. These materials are pretty much ALWAYS available in almost any aquatic habitat any time of year. And fishes are remarkably adaptive to the changes in their habitats which occur with the seasons, and will make use of whatever is available to them for nutrition.

Now, sure, one could state that detritus is the food of last resort for fishes, but the fact of the matter is, it turns up in gut content analysis of fishes caught in all sorts of habitats during any time of the year. It's wildly abundant in aquatic habitats!

SO, where am I going with this?

Well, think about it for a minute. Detritus is sort of the "end product" of the breakdown of botanical materials; it's pretty much a given that you'll find a lot of this stuff in almost any botanical-style aquarium- provided that we don't siphon all of it out in our zeal to create a "perfect" habitat for our fishes. (You can totally SENSE the sarcasm there, right?)

I mean, why do you think our little fishes are typically fat and happy when we come back from vacation and haven't fed them for a week or more? It's because they're foraging on the detritus that's abundant in pretty much any tank- especially in the botanical-style systems we love so much!

Detritus, as I've said like 20,000 times here and elsewhere, is NOT the sign of the apocalypse that authors and armchair aquarium pundits have made it out to be for generations! Nope. Rather, its an important part of the natural diet of many, many fishes! And I haven't even touched on the fact that detritus is a food for a multitude of organisms all along the food chain in aquatic ecosystems- including your botanical-style aquarium!

And what about algae?

And every aquarium, regardless of how scrupulous we are about maintenance- will generate some algae in some manner. Of course it does, because algae is the basis for virtually every aquatic ecosystem, right? And, in addition to being abundant, it's nutritious.

Botanical-style aquariums, filled with nutrients from decomposing materials, are a good habitat in which algae proliferate. And with so many surfaces on botanicals for algae to grow, it's a natural food that requires little energy expenditure for fishes to find.

What other foods are easily produced by the botanical-style aquarium? Well, how about biofilms! Described as "Bacterial aggregates" in the breakdowns above, these are ubiquitous in the wild and in botanical-style tanks, and are possibly the easiest-to-obtain food source at all times for so many fishes. Now, in the specific instances above, they made up a very small percentage within the gut content analysis. Why?

Well, think about it.

Fishes like Tetras (the Hyphessobrycon in the above example) tend to preferentially consume small crustaceans, insects, etc. They're considered "micro-predators" by ichthyologists. However, the more abundant materials like detritus and sediments are likely present in the GCA because the fishes are consuming or taking them in while foraging for the aforementioned organisms. A sort of "by-catch", which just happens to be nutritious. Or, filling, at the least, right? 😆

Biofilms, as we've discussed many times before, contain a complex mix of sugars, bacteria, and other materials, all of which are relatively nutritious for animals which feed on them.

Your botanical-style aquarium will virtually automatically "farm" biofilms with little effort. This is truly one of the great "bonuses" for those of us who keep these kinds of systems! A more or less continuous supply of nutritious supplemental food.

An abundance.

And of course, you could certainly cultivate copepods, like "Cyclops, or Amphipods,"Blood Worms", Paramecium, "black worms", Daphnia, etc. as supplemental "in situ" foods, allowed to multiply for several weeks or more before the fishes are added.

I've done this type of thing many times with reef tanks, and more recently, with botanical-style aquariums. It works really well- and I can attribute my success with a number of fishes which have the reputation of being difficult to feed by embracing this idea! And it gives newly-hatched fishes a "leg up" to gain valuable nutrition before you commence feeding them directly!

Having an abundance of these in situ food sources in your botanical-style tank makes it much easier for wild-caught fishes to adapt to a captive environment, IMHO. I mean, it's not the whole ball game, of course. However, it's one less stress- one less hurdle- to overcome to achieve success with some wild-caught species.

Interestingly, there are a fair number of situations where fishes- even non-herbivorous species- will consume stuff like leaves and other plant materials when their primary foods aren't available. This ability to switch feeding as foods are available is remarkable adaptation,

blackwater systems do show seasonal fluctuations, such as lakes and watercourses enriched with overflow in spring months. At low water levels, the nutrients and population of these life forms are generally more dense.

Creatures like hydracarines (mites), insects, like chironomids (hello, blood worms!), and copepods, like Daphnia, are the dominant fauna that fishes tend to feed on in these waters. This is interesting to contemplate when we consider what to feed our fishes in aquariums, isn't it?

There's a lot of food out there, for the fishes willing to look for it...which, pretty much all of them devote most of their lives to doing, lol

It's not really that much different in the aquarium, is it? I mean, as the leaves and botanicals break down, they are acted upon by fungi and bacteria, the degree of which is dependent upon the available food sources. Granted, with fishes in a closer proximity and higher density than in many wild systems, the natural food sources are probably not sufficient to be the primary source of food for our fishes- but they are one hell of a supplement, right?

That's why, in a botanical-rich, leaf litter dominated aquarium, you see the fishes spending a lot of time foraging in and among the litter...just like in nature.

There is something oddly compelling to us when we look at both aquariums and natural biotopes with a diverse, interesting botanical structure. You set the stage with wood, plants, and then enhance it even more with botanical materials.

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 animals 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?

With so many options for providing realistic natural conditions for our fishes, it seems just painfully obvious that we can look to the whole picture and think of ways to replicate the abundance of natural foods that also occur in our aquariums if we let them.

I'll say it one more time, because I absolutely believe it:

Of all of the things we do in our blackwater/botanical-style aquariums, one of the few "basic practices" that I think we can actually allow Nature to do some of the work on is to provide some sustenance for our fishes.

I think that, as we evolve into the next "era" of botanical-style aquarium practice, we'll see more and more interesting collateral benefits and analogs to the functions of natural aquatic ecosystems. We need to explore these characteristics and benefits as we develop our next generation of aquariums.

Nature offers us an abundance of foods, many of which are already present in our aquariums.

Way not take advantage of what Nature offers us?

Stay thoughtful. Stay observant. Stay diligent. Stay curious. Stay dedicated...

And Stay Wet.

Scott Fellman

Tannin Aquatics