August 08, 2016

On today's menu... Thoughts on leaves and botanicals as food and a "food production zone"

With the enthusiasm increasing almost daily for using botanicals in aquariums, there are all sorts of angles to be worked- assumptions to be reviewed, and yeah, even "myths" to be debunked- relating to their use.

In pervious installments of this blog, we've literally beaten the crap out of the many assumptions that have been made about the "antibacterial" and "antifungal" properties attributed to Catappa and Guava leaves, among others, and have addressed the impact that utilizing leaves and other botanicals has on the closed aquatic environment. We've talked about the collateral activity that accompanies their use (i.e.; formation of biofilms, algae and support of benthic life forms). We've looked at many different attributes of their use as both "functional" and "aesthetic" aquascaping "props", and how fishes interact with them.

One thing that haven't really played with much during our explorations of aquatic botanicals is their use as food- or more specifically, supporting fishes as both a direct feeding mechanism, as well as via the life forms they support. Yeah, exactly...food. Now, we have briefly talked about how decomposing leaf litter does support population of infusoria- a collective term used to describe minute aquatic creatures such as ciliates, euglenoids, protozoa, unicellular algae and small invertebrates that exist in freshwater ecosystems. Yet, there is much to explore on this topic. It's no secret, or surprise- to most aquarists who've played with botanicals, that a tank with a healthy leaf litter component is a pretty good place for the rearing of fry of species associated with blackwater environments!

In general, blackwater environments are often referred to as "nutrient poor", or having little in the way of planktonic life forms. We'll hit the "nutrient poor" thing in a future piece, but today, let's talk about the thinking that blackwater systems are relatively devoid of planktonic life. This is a fact borne out by many years of study by science. However, "impoverished" doesn't mean "devoid" of life. And in many cases, these populations of food organisms do vary from time to time.

Major rivers like the Rio Negro are often called "impoverished" by scientists, in terms of plankton production. They show little seasonal fluctuations in algal and bacterial populations. Other 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? Hmm...Why don't more commercial fish foods contain mostly aquatic insects? Hint, hint, hint, hint...

Anyways, these life forms, both planktonic and insect, tend to feed off of the leaf litter itself, as well as fungi and bacteria present in them as they decompose. The leaf litter bed is a surprisingly dynamic, and one might even say "rich" little benthic biotope, contained within the otherwise "impoverished" waters. And, as we've discussed before on these pages, it should come as no surprise that a large and surprisingly diverse assemblage of fishes make their homes within and closely adjacent to, these litter beds. These are little "food oasis" in areas otherwise relatively devoid of food. The fishes are not there just to look at the pretty leaves.

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 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-rish, leaf litter dominated aquarium, you see the fishes spending a lot of time foraging in and among the litter...just like in nature.

It's been observed by many aquarists, particularly those who breed loricariids, that the fry have significantly higher survival rates when reared in systems with leaves present. I'm sure some success of this could be attributed to the population of infusoria, etc. present within the system as the leaves break down. 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. It therefore would make a lot of sense that a botanical-influenced aquarium with a respectable growth of biofilm would be a great place to rear fry! Maybe not the most attractive place, from an aesthetic standpoint- but a system where the little guys are essentially "knee deep" in supplemental natural food at any given time is a beautiful thing to the busy fish breeder!

And what of the leaves themselves? Do our aquatic animals feed on them? Well, yes- and no. Some fishes, for example, Loricariids, will feed on some of the materials directly, rasping off surface tissues. Others, like certain characins (notably, Headstanders, Metynis, and similar fishes), will feed off of the algae growth, or aufwuchs, as it's collectively referred to, present on the botanicals and leaves. Other creatures, such as the beloved ornamental shrimp (Neocaridina, Caridina, etc.) feed on the biofilms, algal material, and directly on the leaves themselves. Thus, I am a big fan of including some of these creatures in a blackwater, leaf-litter-dominant display! Not only do they do very well in such systems, in my experience- but they can help keep the biofilms from getting too much of an "upper hand" in such an aquarium.

Okay, I've gone on and on about this today...I think I've at least scratched the surface on the subject of botanical-rich aquariums being beneficial to their inhabitants because of the supplemental food system they both provide and support. I think that it is definitely worthwhile for more experimentation to be conducted by fish breeders, who are in a unique position to see for themselves exactly how the presence of leaves and other botanicals in rearing tanks can influence both the survival and growth rate of fry. Who is up for the experiment?

As always, there is SO much to learn about this stuff; one person, or even a small group of people- can't do it all. I hope that I've at least whetted the appetite (no pun intended, here) of some of you talented and engaged hobbyists to play around with this stuff a bit more!

Until next time- Keep experimenting. Stay curious. Stay innovative. Stay adventurous.

And Stay Wet.

Scott Fellman

Tannin Aquatics