I've talked so much about how great botanicals like leaves, seed pods, etc. are for aesthetics and creating optimal environmental conditions for a variety of fishes over the past couple of years, and only really touched briefly on the concept of incorporating them in tanks for rearing of fry.
I really like the idea of a botanical-influenced "nursery" tank for blackwater fishes for a number of reasons:
First, as we've discussed many times, the humic substances and other compounds associated with leaves and other botanicals, when released into the water, are known to have beneficial health impact on fishes. The potential for antimicrobial and antifungal effects is documented by science and is quite real. Wouldn't this be something worth investigating from our unique angle?
I think so!
Additionally, rearing young fishes in the type of environmental conditions under which they will spend the rest of their lives makes a lot of sense. Having to acclimate young fishes into unfamiliar/different conditions, however beneficial they might be, still can be stressful to them.
Why not be consistent from day one?
Finally-and this is the aspect we're going to focus on the most here- the breakdown and decomposition of various botanical materials provides a very natural supplemental source of food for young fishes, both directly (as in the case of fishes such as xyliphorous catfishes, etc., and indirectly, as they graze on algal growth, biofilms, fungi, and small crustaceans which inhabit the botanical "bed" in the aquarium.
Now, this is pretty interesting stuff to me. Everyone has their own style of fry rearing. Some hobbyists like bare bottom tanks, some prefer densely planted tanks, etc. I'm proposing the idea of rearing young fishes in a botanical-style blackwater aquarium with leaves, some seed pods, and maybe some plants as well. The physically and "functionally" mimic, at least to some extent, the habitats in which many young fishes grow up in.
My thinking is that decomposing leaves will not only provide material for the fishes to feed on and among, they will provide a natural "shelter" for them as well, potentially eliminating or reducing stresses. In nature, many fry which do not receive parental care tend to hide in the leaves or other biocover in their environment, and providing such natural conditions will certainly accommodate this behavior.
Decomposing leaves can stimulate a certain amount of microbial growth, with infusoria and even forms of bacteria becoming potential food sources for fry. I've read a few studies where phototrophic bacteria were added to the diet of larval fishes, producing measurably higher growth rates. Now, I'm not suggesting that your fry will gorge on beneficial bacteria "cultured" in situ in your blackwater nursery and grow exponentially faster. However, I am suggesting that it might provide some beneficial supplemental nutrition at no cost to you!
And it's the same with that beloved aquarium "catch all" of infusoria. These time-honored organisms are likely to arise whenever plant matter decomposes in water, and in an aquarium with significant leaves and such, there is likely a higher population density of these ubiquitous organisms available to the young fishes.
Now, I'm not fooling myself into believing that a large bed of decomposing leaves and botanicals in your aquarium will satisfy the total nutritional needs of a batch of characins, but it might provide the support for some supplemental feeding!
I'd take the concept even a bit further by "seeding" the tank with some Daphnia and perhaps some of the other commonly available live freshwater crustaceans, and letting them do their thing before the fry arrive. This way, you've got sort of the makings a little bit of a "food web" going on- the small crustaceans helping to feed off of some of the available nutrients and lower life forms, and the fish at the top of it all.
Now, granted, I'm romancing this and perhaps even over-simplifying it a bit. However, I think that there is a compelling case to be made for creating a rearing tank that supports a biologically diverse set of inhabitants for food sources.
The basis of it all would be leaves and some of the botanicals which seem to do a better job at recruiting biofilms- the "harder shelled" stuff, like "Save Pods", "Jungle Pods", Coco Curls", etc...I think these would be interesting items to include in a "nursery tank." And of course, they provide shelter and foraging areas and impart some tannins into the water...the usual stuff.
Just another one of those ideas that would be fun to experiment with. Certainly not the "ultimate" fry rearing system...but I think one worth experimenting with!
Stay creative. Stay curious. Stay adventurous. Stay diligent. Stay excited...
And Stay Wet.