I've got another thread going regarding this in
freshwater fish Disease, but I wanted to answer you, 0morrokh.

I found a dead danio (the other male!) today, so it must be affecting my danios as well as my otos. (Whatever Georgie had affected everyone, obviously.) I don't know what to do. Other than not eating when I fed them today, the danios are acting "normal." They are darting around chasing one another. During the few seconds they stop, I am not able to see any abnormalities on their bodies. I just don't get it. I am so stressed out!!
Oh, and I WAS going to get a q tank (don't have one yet) but we'll see what happens to these 2 remaining fish...I may just have to start over!
Sharon