Actually, I tried to catch him to take him back to the LFS -- and he knew we were aiming for him. And when I couldn't catch him (how could a fish that big hide so well??) I asked a friend who "communicates" with animals to talk to him. Yes, I know, very weird. But I was desperate. She was a bit skeptical and said she'd never talked to a fish before. Anyway, she did her best and I swear, he calmed down after that and was never a problem again. (I also moved some rocks around when chasing him, so maybe that was it!)