For the most part it is best to keep kind with kind, however there are some species (arboreal that I am thinking of) that are immune to fire bellies toxin although your tank is probably too small too house them comfortably. Pertaining to fish in the water. I also had some baby guppies hatch probably from plants in the 6 inches or so of water I have with my firebellies-I have seen at least two of my toads fish crickets and guppies from the water. A woman at the pet store told me she uses guppies and white clouds as feeders and also some of her toads will fish them from water. =)