I think any of the 3, dovii, umbee or jaguar would be about the meanest things you can get, but each fish has its own personality. I have also had a mean Blackbelt before and a Green Terror that really lived up to its name! I mostly keep single fish so I don't see a lot of fighting in my tanks. My jaguar hybrid bites like a piranha, whenever I have to fix filter tubes or change water. I've seen him eyeing my cat's tail (feline) whenever it gets dangled into the tank.