December 12, 2017

"Wood" you believe...? Yeah, there's more to it than that!

One of the things I tend to think of a lot in my daily aquarium practice is the dietary requirements of our fishes. And, not just what to toss into the tank...Rather, how to actually construct the tank and aquascape themselves to be a part of the feeding process.

Huh?

Lately, I've been giving more and more thought to the way that our fishes tend to feed...specifically, thinking about our botanical-style tanks not only as a "structural-aesthetic" vehicle, but from the perspective of providing the fishes which reside in them supplemental food sources.

And it goes even beyond even the "refugium" concept we've talked about- purposely cultivating aquatic crustaceans, microorganisms, and insects somewhere within the system to supplement the foods we're feeding our fishes. Yeah, it's about configuring the aquarium hardscape itself to serve as a supplemental food source. Sure, we all know about the benefits of biofilms and epiphytic algal growth on our wood and botanicals- but what about the wood and botanicals themselves being a food source?

Well, sure- there is plenty of precedent for this in the aquarium hobby. Just about anyone who has more than a casual interest in Loricariids knows that many tend to feed directly on wood, earning the title of "xylivore" (an organism which feeds on wood). And it's also been documented through gut content analysis that these fishes are not only rasping the wood and consuming some of the outer layers- they're also taking on the biofilm and layers of micro and macro organisms which reside in and on the wood itself. What are these other items? And what kinds of wood materials are these fishes preferentially consuming?

Well, gut content analysis of Panaque nigrolineatus from one study I perused showed a dominant presence of a coconut wood (Scheelea phalerata)! This makes us think about utilizing materials that are coconut-derived, in addition to the regular driftwoods we use in aquascaping. It's not just having some wood in the tank for these fishes to graze on...my thinking is that it may be equally important to have the right kind of wood materials for them to graze upon. Bring on the "Coco Curls!"

And while we're on the subject of Loricarids, a scan of scientific literature reveals some interesting things about what these fishes are actually taking in when they "graze" in the wild. It's kind of eye opening, to me. One study revealed that Loricariids consumed five principal items: sponges, organic detritus, bryophytes, bryozoans and sediment. Wood is definitely part of the equation, but for the species examined in one of the studies I found (Rhinelepis aspera, Hypostomus regani, H. ternetzi, H. maragaritifer, H. microstomus, and Megalancistrus aculeatus) the gut content analysis was quite revealing:

The food spectrum of R. aspera is primarily organic detritus and small quantities of sediment; with few periphytic organisms. Although H. regani was found to consume large quantities of organic detritus as well, it also consumed plant detritus, various sediment, and periphytic organisms (i.e.; bryozoans, sponges and aquatic insect larvae). Bryozoans and sponges, huh? Wow! The study indicated that bryozoans and organic detritus were the main food food of H. ternetzi, which, according to the gut contents of a number of individuals, tended to consume more sediment, rotifers, chironomids (i.e.; "Bloodworms'), gastropods and harpacticoids than the other species. Harpactoids...you mean, like "copepods? Stuff we as reefers feed all the time? H. margaritifer was found to ingest plant material. Other periphytic organisms such as insect larvae, and those bryozoans and sponges contributed to the diet of H. margaritifer.

And it gets more interesting still...

Sponges were the principal food resource of H. microstomus and M. aculeatus, with a healthy does of chironomids, various gastropods, Trichoptera (insects), and some bryozoans also consumed. Diets of these two fishes were composed of larger-sized items, with the finer organic detritus and such being less important than it was to the other species in the study.

This kind of information is tantalizing. It's compelling. And what really gets me going is learning that some of our favorite, most beloved fishes are consuming large quantities of materials that I doubt any aquarist adds to his/her arsenal of foodstuffs. We're really good at feeding our catfishes baby vegetables and stuff, while typically overlooking many species surprisingly high dietary dependency on items like insects, bryozoans, harpactoid copepods, and interestingly...sponges!

While we kind of always knew that these fishes consumed wood and "stuff", it's interesting to see what they're eating in the wild...especially the "stuff"- and configuring our aquariums and the supplemental and primary feeding opportunities available to the fishes accordingly. We have some interesting, yet perhaps overlooked possibilities to provide some of these items.

Now, interestingly, there are a number of marine aquarium-purposed foods (typically targeted at marine angelfishes, many of which consume significant quantities of sponge) which contain sponges in their forumlation. Granted, these are marine sponges, but I can't help but wonder if these are that morphologically or nutritionally different to the fishes than a freshwater/tree sponge would be? Could the next great frozen Loricarid food include sponges? And we have harpactoid copepods available live and in a variety of other formats intended for marine organisms...Interestingly, the big "knock" by reefers for a long time about some of these copepods was that they were "freshwater" varieties...Hmm...

(Image by Copepodkils used under CC-BY SA 3.0)

So really, the takeaway from this little rambling thingy is to really go just beyond what we know, even when it comes to well-studied (hobby-wise) fishes like the "Plecos", which have been kept and bred for years. Sure, we're doing really well..Seems like we could even do better with just a few dietary "tweaks", right?

So, don't fear detritus. Be daring enough to try feeding some sponge-based frozen marine aquarium foods. Oh, and perhaps try some marine-intended cultures of harpactoid copepods...Or even figuring out ways to cultivate freshwater sponges...Possibilities.

And unrelated to this....something to contemplate and think about: There ARE actually fishes which consume leaves as a part of their diet... And more fishes than you think actually eat fruit, too. Yup.