it may seem like just an oddity, but i have learned some important things about certain fish fry by watching them under a microscope. the Elassoma gilberti fry are nearly microscopic when they hatch, so its hard to know what food to feed them without taking a really close look at them. another hobbiest who breeds them raised them on microworms, but when i started getting fry a couple months ago they seemed too small to eat the microworms. after looking at them under the scope, it was pretty obvious that most of the microworms were too big for them. not only that, but their mouth isnt even developed enough to eat anything until they are about 8 days old.
what i found out was that the fry werent able to eat most of the microworms, so most of the worms would die and contribute to declining water quality, which was killing the fry. i also learned that if you leave daphnia ambigua and attempt to feed them the young that the daphnia produce, the young daphnia produce a much larger apical spine after just a couple molts. i saw one fry attempt to eat one, but the larger apical spine(response to kairomones produced by the fry) got caught in its mouth and ended up killing it.
that taught me that if i wanted to feed young daphnia ambigua(worlds smallest daphnia) to them as a first food, i have to raise them separate and feed only the young to them, then do a water change to remove the uneaten daphnids. even though they werent fouling the water, they would still kill the fry.
i know it is common practice to change water religiously when raising fry, but im not one to take advice for granted and just do it. i always ask why, then set out to determine why. as it turns out, i found out that constant water changes is NOT the best way to raise gilberti fry. after observing some of my fry eat small rotifers and various ciliates, i set up a few tanks to see what was really going on. i split up my 30 or so fry into three different groups and raised them in different conditions. in one group, i fed them nothing at all and only topped off their container with filtered tank water. in another group, i fed them nothing but tank water that was rinsed from some hair algae i had cultured, changing a little of the water each day. in the last group, i changed nearly all the water each day and fed them the same rinse water as group two. my goal was to determine how the conditions of the growout containers were affected by these different water change regimes. group one had 8 fry survive until free swimming, group two had three fry survive, and group three had none. all three groups were kept under 24 hour lighting.
looking water samples from the three containers, group one had cyano and ciliates everywhere. group two had the same, but also seemed to have an over abundance of cyano, some of which had formed layers and died. group three seemed a lot like group two, except the cyano had a lot more old growth under it.
with the next batch of fry i tried the same thing under normal light routines, in which the highest survival rate came from group three. still, only 3 survived from that group, the rest died from apparent water quality issues(since they were still too young to eat anything). the containers they were tested in were ten cm long, eight cm wide, and three cm deep. these fry are small enough to easily get lost in a container that large. here is an example;
there are FIVE gilberti fry centered on the dime in this pic:
i have only been getting fry from them for the last three months, but i feel like i know enough now to achieve much higher than normal survival rates. for this species, it seems that for the first couple weeks, you can leave them alone as long as there is a little infusoria for them to eat and the water quality does not decline. under 24/7 lighting, a thin layer of cyano will grow, which decreases ammonia and raises oxygen. turn the lights off, however, and the cyano depletes oxygen and dies back a little and degrades water quality. its just simpler to keep the lights on 24/7 and not do any water changes until the fry are large enough to eat something a bit more substantial. in shallow water i suspect that algae and cyano can supersaturate the water with oxygen, which in of itself can boost survival and growth rates. i have not yet tested that idea though.
well i think ive rambled on long enough...
