Wedge-tail triggerfish (Rhinecanthus rectangulus). X-ray of a section through a wedge-tail triggerfish, showing its dorsal spines (top centre). Triggerfish (family Balistidae) discourage predators by erecting two sharp dorsal spines: a large, thick one and a shorter spine behind it. The second spine is the 'trigger' and locks the first one in place. This species is endemic to the salt water coasts of various central and south Pacific Ocean islands. This specimen measures 15 centimetres in length.