Saddleback Butterflyfish are a rare but beautiful sight on Maui. They can surprise a snorkeler or diver by suddenly popping their heads up over a high coral reef or emerging from a silty fishpond.   They feed on everything from coral polyps, small crustaceans and invertebrates, to algae. They can be quite skittish and usually travel in pairs. A lone mature Saddleback generally signals the loss of a partner. Seeing more than one pair traveling together is . . . well, almost unheard of in the Main Hawaiian Islands.  Up to 12 inches.   Click here for more details re threats, habitat and habits.