If I'mnot mistaken, at least some of the soft shells, like the florida species need to bask in order to digest food, not sure about the others. The only other turtle that I know of that is fully aquatic or at least can be is the snapping turtle or the alligator snapping turtle. Not sure how they would mix with your stock. I've never kept them and I know that the will eat all small that will fit in their mouths, but I don't know about biting at larger fish. CB= captive breed.