Lagoon Triggerfish

The lagoon triggerfish is a vividly patterned reef fish — yellow, blue, black, and white stripes on a deep, laterally flattened body — famous for two things. First, it swims by rippling its dorsal and anal fins rather than its tail, which lets it hover and reverse with precision. Second, it defends its nest fiercely: divers and swimmers who stray near a nesting site can be chased away, sometimes persistently. Its common name comes from a locking spine on the back that the fish ‘triggers’ upright to wedge itself into reef crevices overnight.