Any type of fish has the ability to become aggressive, however there are certain specimens which have been labeled "agressive" much like the Pitbulls of the dog world. From my personal experience I have seen very aggressive Triggers but at the same time very passive triggers. Same goes from Moray Eels, Sharks, Angels ect. I guess it all depends on the fish its self, however Moray Eels such as the Tessalata and the Green Moray have the power, size, and temper to be one of the most aggressive Marine fish, along with Sharks ofcourse if provoked, oh ya cant forget triggers. I tend to find triggers more of a pain than aggressive however.