triggerfish

Any marine bony fish of the family Balistidae, with a laterally compressed body, up to 60 cm/2 ft long, and a deep belly. They have small mouths but strong jaws and teeth. The first spine on the dorsal fin locks into an erect position, allowing them to fasten themselves securely in crevices for protection; it can only be moved by depressing the smaller third (‘trigger’) spine.

There are many species, found mainly in warm waters, and some are very colourful.