Lately, I've been giving some further thoughts to fish feeding. The traditional approach is commercial pelletized or flake product, manually administered once or twice a day. My plans thus far (for an omnivorous species mix of tilapia and catfish) include a diet of fresh duckweed, red wriggler earthworms, some table scraps, and seasonal dead bees (no idea yet how they'll go over). I highly suspect that the sum of this will still not be sufficient. I also prefer that the feeding mechanism be somewhat automated, so that I might have the occasional luxury of being absent for a few days or weeks at a time, without having to enlist a fish sitter.

For the duckweed, which I envision as the base of the fishies' dietary pyramid, I was thinking of having an additional sump located above the fish tank where the duck weed would grow, and periodically overflow into the fish tank. My preference is for a purely hydraulic timing mechanism such as a bell siphon, but will need to think some more on how to achieve a twice daily spillover without otherwise impeding the steady cycling of water needed for oxygenation. I'll probably also want something that is adjustable, so that if my flow rate (dependent on my sump pumps) changes (if for instance I expand the system), my feeding schedule can be consistent.

I've also been considering the addition of a buffer species in the food chain such as Hyalella azteca, which might also act as "canaries in the coalmine" for chemical and temperature imbalances. These tiny crustaceans eat primarily algae and diatoms so I'd need to provide (mainly light) for those species as well. Most aquarium enthusiasts and aquaponists view algae as anathema to their systems, with the understanding that dying algae deplete dissolved oxygen and add nitrates to the water. Live algae should theoretically be net oxygen producers, but I suspect that there must be something to keep it in check (enter the amphipods) to avoid unstable population spiking. Although it's not a true algae, I'm hoping spirulina will work. I have no references yet for aquarium grown diatoms but would love to explore further. I have long been fascinated however by the natural design of diatoms and the practical applicability of eventually developing CELSS along those same lines: two interlocking halves that can split apart and grow into separate organisms. Eventually there will be a need for such reproductive "mitosis" of CELSS (although technically in order to grow, they will need to consume and transmute raw matter into organic structure, just as natural diatoms do, so would no longer strictly be "closed"). Diatoms are also photosynthetic. I know they build their shells from dissolved silicon compounds; how readily these minerals are available in a standard aquaponics system is an open question for me.

Incidentally, my title for this installment pays homage to Stephen J Gould's treatise on bioddivergence in evolution. His chapter of course discusses the spawning of the Reformation movement from its Catholic parentage, in explanation of the titular pun.