Depends, firemouths like to test the aggression of other fish. For example...My 3" FM flares at a 5" Male Black convict.. The convict could kick his ass in a second, but is tolerable of the FM. My FM also flares my 6" jag.. So, imo they got more bark than bite, just gotta be careful, some fish do see that as a threat and will go after the FM. At the same time, individuals are different. As for JD's temperment, I've never had one, and couldn't vouch for em. Hope that helped somewhat.