pip, I think you have a male in your sorority. Those pale vertical stripes on the sides of a dark female are classic breeding stripes, and are very rarely displayed unless an adult male is present. The fact that 11 out of 24 females are displaying them, and also that they're getting eggy, is very suspect. The nipping and aggression is as well, because 24 females (which I am assuming are of similar age and may even have been raised together) added to a suitable tank (your tanks are always suitable, you know what you're doing) at the same time would be expected to show very little aggression. Also, the female in the pic looks very stressed. Faint stress lines, splayed posture of the fins and the alert expression even though she's resting and looks exhasted. Hard to explain what I'm looking at really but the way she's sitting is saying to me 'I'm scared'.
I could be wrong but just have a look... unless you got these females directly from a breeder you trust, a plakat showing up in there wouldn't be the least unusual.
