Fish I have bought and will never buy again? Only one really springs to mind, Batrochoglanis raninus (common name of Bumblebee Catfish). Not that he wasn't a stunning little fish. He just grew VERY quickly (3 inches in the first month I had him) and soon after that, ate anything that fit in his mouth (which ended up being a number of my fish). I completely expected that to happen, just thought the other fish were big enough he wouldn't bother them yet. He was a "rescue" or sorts (the shop where I found him often gets "mystery fish" in with shipments, fish they didnt' order and aren't sure what they are, though I recognized him right away, figured I'd give him a better home than some poor unsuspecting kid). I found some monster keepers to give him a right proper home after that, but I enjoyed him while I had him. Now, maybe if I were to somehow be able to afford a very large tank and large tankmates, I might reconsider, as he was a truly interesting fish to watch.