My tank consists of ~40 endlers from fry to adults, 10 albino cories, 4 panda cories, and four billion trumpet snails. There were originally 10 pandas, but one by one their tails became chewed up and they died off. Now I have an albino with a chewed tail, a bloody hole where his right gill cover used to be, and a missing right barbel.
The tank is two years old, parameters are steady and normal, and no purchased fish have been added in several months. (Endlers are born in the tank continuously.)
I've always known cories to be passive, so I blame the endlers. My husband thinks they targeted the pandas because their coloring is similar to the female endlers, but now that an albino is injured, that theory no longer stands.
The only pattern I see is that I notice damage after a frozen feeding, as opposed to flakes. Perhaps this makes them more aggressive? Or perhaps they are getting in each others' way, since frozen food sinks and the flakes float? I'm not sure what to do if this is a problem. I want to feed a varied diet, but obviously causing injuries isn't acceptable.
Has anybody known these bitty things to be mean? I find it hard to believe they're roughing up fish five times their size, but I've run out of suspects.