Hello there! i have one of those hermit crabs, they are a pretty cool specimen to own and have. if you actually feed the hermit crab its own piece of food, (i give mine quarter of a frozen silver side per week and mine is roughly 2.5" out of shell) i have found he leaves the other fish alone. there are some reports of these hermit crabs preying upon smaller and slower fish, but i have a blenny and several other fish in there with him and he hasnt eaten one yet. the only harm he may do is if a fish tries to nip on the food that you gave him away he will smack it with his claws and that slightly injured a damsel of mine but hes ok. they are very hardy and do a decent job of gravel cleaning. im sure if you started smaller itd be a fine addition to your tank. Cheers!
