Unfortunately not uncommon. Male Trichopterus trichogaster (including blue gouramis, yellow gouramis, and any number of other varieties) simply aren't good community fish -- they're aggressive, territorial, and short-tempered. The size of the tank is a big factor, and they go for "similar" fishes (i.e., not just their own species but also angelfish, dwarf gouramis, etc.) most of all. But still, best avoided or else kept in tanks with robust species either too heavily armoured to be damaged or too fast to be caught.Cheers, Neale
He has killed two other fish, does this mean that he needs to be by himself?