My son has a viquarium containing about 5 gallons of water, and a large, cannibalistic, african clawed frog. Needless to say, any small fish that we add are a tasty treat for the frog. My son recently saw some freshwater crabs as well as some electric blue crayfish, and would like to add them to the tank. Doe anyone know whether this combination would be at all compatible? Or would some inhabitant perish?