He was the Heavyweight Champion of the World from 1919 to 1926.
Provided the tank is large enough and the fish are of a similar size there should be no proplems until a couple pair off and decide to breed. Then, if you don't have the facilities to house either...
It is the size of the food fish that matters. Even a baby Jack Dempsy will eat any live fish small enough to fit into its mouth.
Dempsey was the Undisputed Heavyweight Champion from 1919 to 1926.
BoxRec has 6' 1" Ring Record Book has 6' 0-3/4"