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Overview

Coral reefs are the result of millions of years of coevolution among algae, invertebrates and fish. They have become crowded and complex environments, and the fish have evolved many ingenious ways of surviving. Most fishes found on coral reefs are ray-finned fishes, known for the characteristic sharp, bony rays and spines in their fins. These spines provide formidable defences, and when erected they can usually be locked in place or are venomous. Many reef fish have also evolved cryptic coloration to confuse predators.

Reef fish have also evolved complex adaptive behaviours. Small reef fish get protection from predators by hiding in reef crevices or by shoaling and schooling. Many reef fish confine themselves to one small neighbourhood where every hiding place is known and can be immediately accessed. Others cruise the reefs for food in shoals, but return to a known area to hide when they are inactive. Resting small fish are still vulnerable to attack by crevice predators, so many fish, such as triggerfish, squeeze into a small hiding place and wedge themselves by erecting their spines.

As an example of the adaptations made by reef fish, the yellow tang is a herbivore which feeds on benthic turf algae. They also provide cleaner services to marine turtles, by removing algal growth from their shells. They do not tolerate other fish with the same colour or shape. When alarmed, the usually placid yellow tang can erect spines in its tail and slash at its opponent with rapid sideways movements.