And, as to the minimum tank sizes, especially those in Scott Michael's books, I think there should be a distinction between minimum tank size for survival and minimum tank size for what we would consider ethical. The reality, IMO, is that most sharks and rays that are common in the aquarium trade are pretty hardy and resistant to disease. Most can survive in tanks smaller than we commonly associate with being appropriate. Most disagree with the tank sizes, though becuase we don't consider keeping these guys in smaller tanks to be humane to the animal.