I've kept them in pure fresh for up to three years and up to 10" long, they really do seem to do best with live food, Daphnia magna is my live food of choice but live black worms are eaten like crazy too. I'm not sure but I think that living in pure fresh causes them to need more food, at least mine ate like crazy on live food but were never all that good about eating dead stuff. Keeping them on dead stuff always seemed to mean very few lived. The do have problems competing with other fish for dead food but become aggressive feeders with live food. Adults do indeed need salt water, at about two to three years and 10" they die with out a marine set up.