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Seemingly random thoughts I have during water changes...

Tannin Aquatics

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I love water exchange days.

There is something...I dunno- visceral about doing something that you know is beneficial for your animals. It's not only a "feel good thing", it helps foster a sense of connection between man and nature. Or at the very least, it makes your tanks sparkle! 


I liken my weekly water exchanges to rain storms in the tropics. They "refresh" the waters, add new trace elements, ions, and in our case, tannins, helping to keep the environmental parameters consistent, while purging them of metabolites, impurities, and pollutants. It sort of does the same thing to my mind.


While I'm doing my water exchanges, I am in an almost "meditative", relaxed state, which gives me the opportunity to reflect on various topics that interest me...stuff that, of course, form the basis for my rather "stream-of consciousness" blogs- like this one!

Today, I was reflecting upon the most simple of topics- one which we think about a lot, I'm sure: What our fishes eat, and how they eat in the wild.


Ever think about what your fishes eat in the wild? But beyond that, what implications do their dietary preferences have for those who want to mimic them as closely as possible?

Yeah, it's easy to say "insects and stuff" and move on, but the reality is that, even for some of the most unlikely fishes, the variety of items they consume is astonishingly diverse, and perhaps unexpected!


Of course, I had to get down and dirty and do some online research...And I found some interesting stuff. For example, one study of the gut contents of that rather well-liked characin, the Cardinal Tetra (Paracheirodon axelrodi) in it's natural habitat yielded some familiar food items, and perhaps, a few surprises:

Harpactoid copepods (you know, like the kind we use as food for marine fishes), Daphnia, Moina (another small, Daphnia-like microcrustracean), nymph larvae,  small flies of various species, partially digested ants (!). In addition to being a surprising find, the presence of ants and flies in the fishes' digestive systems confirms that they may feed from the surface in the wild, too! So those flakes we toss in are recognizable to these guys, perhaps not because they resemble food or smell good, but because these fishes will dart to the surface and feed in the wild!


What else did the study find? Rotifers, crustacean larvae, and crustacean and fish eggs (Ahh, my case for Doc's Eco Eggs, which is Capelin roe, as a supplemental food, is looking even better!)! Some filamentous algae and diatoms were also found, further bolstering the idea that although we tend to classify fishes like characins as "micro predators", they are also opportunistic ominivores to some extent, foraging for what they can in the environments in which they reside. And, then, random "detritus", including things like fish scales and such, which you could hypothesize might mean that they either pick at other fishes, or forage on dead ones...yuck.

What does all of this stuff mean for us as hobbyists? Well, I'm not saying to drop ants into your tank (although it is tempting, if not a bit vengeful). What I am saying is that a diverse menu of plant an animal material is always a good idea, and the bulk should be things like crustaceans, insect larvae (hey- bloodworms!), and even some of the live or frozen copepods, and stuff like Daphnia would make a diet that is a pretty good mimic of what they consume in the wild, right?


And maybe that old, yet annoyingly-messy-to-culture standby, the Wingless Fruit Fly, might not be a bad food source?


Another interesting thing I found in my research was that when scientists studied some Amazonian leaf litter beds, it was found that, in one study, there were like 20-plus species found in one bed of like 200 square meters- a remarkable diversity considering the rather specialized environment. And perhaps more interesting was that the bulk of the species found were feeding almost exclusively on the invertebrate life present in these liter beds, seldom straying more than one meter (!) from where they were initially captured. Talk about going where the food is!


As there are finite resources of food, even in an area as productive as a submerged leaf litter bed, and because there is such a diversity of species in such a small area, it was theorized by researchers (Henderson and Walker) that fishes have developed what they termed "refined habitat subdivision." In simple terms, this means that each species has evolved to feed on a separate resource supply to avoid "competitive deprivation" of the food sources. The prey doesn't move, either- like chironomids (an insect-like creature) that comprise a lot of the fishes' diets, remain attached to the same leaf for their entire life cycle! So you see where this is going? Each fish inhabits a spatial niche within the litter, feeding on it's own localized food supply.


Well, at least I found this interesting!

Again, what are the aquarium-level takeaways here? Well, since we can get food to our fishes regardless of what level they inhabit within our aquariums, it is entirely logical to create fish communities where the species selected inhabit different areas of the tank (okay, leaf litter bed, in my obsessive fish-geek case). So for example, a good combination of fishes in a leaf-litter-themed tank would include Apistogramma, which in nature seem to hang out at the edges of the leaf litter beds, various characins in the "middle" of it all, and fishes like Pencilfishes and Pyrulina holding station above the litter bed (I see this in my own tanks). If one could ever secure my obsession fish, the cryptic, darter-like characin, Elachocharax pulcher, they'd reside right smack in the middle of the leaf litter! Ahh..


Okay, so anyways, to wrap up this meander- you can see that feeding is just one consideration you can think about when stocking an aquarium. Not only what to feed, but where...Think about preferred feeding niches for various species in the wild when stocking. Now, granted, in an aquarium, fishes will adapt and typically  feed wherever the food is- but wouldn't it be an interesting experiment to set up a population of fishes that you know feed in different locales, and actually creating those locales for the fishes? Maybe? No? Possibly? Okay, whatever. Geeking out here...


Anyways, that's the kind of stuff I ponder while doing my water exchanges- in addition to the age-old question of wondering why my feet are getting wet if the end of the siphon hose is in the bucket....and that's another subject for another time.

So, stay contemplative. Stay curious.

And Stay Wet (except when you're siphoning water!).

Scott Fellman

Tannin Aquatics

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