I'd kept the two fish in an isolation breeding tank for the first week and when I came to move them to their main tank I noticed the smaller fish wasn't swimming actively and had a small red area (on the white) close to it's tail.
The red mark rapidly progressed and the entire rear (previously white) half of the fish became a blood red and within 6 hours the fish was dead.
Initially I blamed myself, for when I was moving the fish I'd accidentally collapsed a cave and I assumed I'd crushed the fishes tail causing internal bleeding and death.
However, I've just been surfing this site and I've seen a few posts that suggest the red colour is a stress reaction? I replaced the dead fish with another expensive fish from the same shop and batch of youngsters so I'm hoping it was a crush injury rather than anything else.
