most likely bufo americanus, your dog was reacting to there venom, which is used as a defense mechanism, the venom is called bufotoxins, and most of the toads in the midwest are only mild at the most, although possibly strong enough to kill a fish, definatly stay away from feeding your large fish toads or salamanders, a tree frog would be much safer but not even sure if that would be recommended, not sure if fish need a significant source of calcium in there diet, if so i guess once or twice a year wouldnt be a bad thing