Mine was incredibly aggressive. He went after anything on ten legs -- pods (eradicated the population), hermits, shrimp, crabs, no matter what their size. He'd lay in wait for fish to swim by and then dart out, striking at them like a cobra. These fish are gorgeous and definitely hardy, but they're also crafty and can be downright vicious. Dottys have been described as the nastiest fish in the ocean, pound for pound. I think that's taking it a bit far, but only a bit -- a neon would make a good tankmate for larger, tougher fish but IMHO they're not suitable for a tank housing any shrimp/crabs or fish such as skittish wrasses, gobies, firefish etc.