I've been breeding albino corydora aeneus for over a year now. I usually lose about 20% to deformity/injury/whatever; recently, however, the death rate has nearly hit 100%.
I raise my fry in a bare-bottomed plastic 5gallon with a bubbler -- if I have several batches on the go, I put the others in ice cream pails with bubblers, clipped to the inside of one of my larger tanks for warmth. The fry eat a mix of powdered fish flakes and hardboiled chicken egg yolk for the first week or so after their yolk sacs are gone, then I gradually change them over to frozen bloodworms chopped very fine with a razor.
About three months ago, I noticed many of my fry developing stringy, fluffy, white "beards" coming out of their gills. These beards are tough -- I cannot pull them out from dead fry's gills with tweezers -- and all the fry that develop them eventually die. As the fry are basically transparent, I can sometimes see part of a bloodworm still in their mouth, so I assumed the beards were chunks of bloodworms that the fry had tried to spit out and had gotten caught in the gills. I have been using the same brand of bloodworms for years, and until this have had no problems. I wrote a letter to the manufacturer asking them if they had somehow made their bloodworms tougher, and am currently awaiting a reply.
I switched my fry to another brand of frozen bloodworms, and the next batch of fry were fine -- until yesterday, when I suddenly lost over 90 of my 107 fry, and the remaining fry now have those fluffy white gill "beards."
The only change I have made in the past few months is removing the small pump I had in the fry 5g 'cause it started making some very nasty noises. Could the removal of the pump result in fry developing gill growths? Am I fostering some sort of weird small-fry disease (fry that survive to about 1 month are not affected; it's just the smaller guys)? Have my fry tanks been infected with mutant-creating radiation??
I would greatly appreciate any ideas or input, as I have a batch of eggs hatching as I write, and I don't want to sentence them to death....
Fungus, of course! Didn't even occur to me. The white stringy stuff seems pretty tough for fungus, but it makes sense -- I do periodically wipe the tank walls down with a bit of sponge and suck up the wads of scungy stuff with a turkey baster, but I haven't been doing that as often as I used to, plus the pump broke down....So it looks like my poor fry have basically been getting infections due to scungy water and low oxygen. Boy do I feel like a dirty rat now.