I put in two 1" convicts in with my fire eel when he was 18" and he never bothered them. When he was about 15" I had him in with a 13" tire track. They grew up together but when they got to that size the fire eel started beating the hell out of the TT and I had to separate them (never any problems till then). I suspect the TT of killing sone of the smaller fish in his tank (sword tails) but leaves everything else alone.