It depends on the which african frog, dwarf of clawed? dwarves absolutely not, I think they would end up as lunch. Clawed frogs are becoming illegal in many states so you may not even be able to get them, but they probably would be ok with convicts. I really don't think the convicts would eat much for feeder fish, possibily feeder guppies but anything bigger would be too much. Feeding live foods though is quite risky, like has been mentioned feeder fish are disease and parasite factories. Feeding other live foods also increases the risk of disease and parasites in the tank. Thus its not generally reccomended. Frozen is fed more often becuase it does reduce the chance of disease, and it keeps much longer than live foods, feed what you want and throw it back in the freezer. Its generally a lot cheaper as well. Another note is that feeding live feeder fish to predatory fish increases their aggression.