Triggerfish

Like chameleons, triggerfish can swivel their eyes independently. This allows them to watch out for predators with one eye, while using the other eye to deal with their own prey.

The triggerfish has an unusual dorsal (back) fin. The fin has two spines; the first one is long and stout, and the second one is shorter and more slender. The dorsal fin normally lies flat. But when the fish is alarmed or needs to defend itself, it raises the first spine. Once raised, the spine helps the triggerfish to wedge itself securely in a small cave or crevice, out of reach of a potential predator. As soon as the first spine is raised, the second spine is also pulled up, and it automatically locks the
first spine firmly in position. The locking system is operated by a bony knob at the base of the second spine. It fits into a hollow at the bottom of the first spine, stopping it from being lowered so long as the bony knob is in position.

Sharp, Spiky Food

Sea urchins form a big part of a triggerfish’s diet; in spite of the fact that the urchins’ bodies are well protected by spines, and may be able to inject poisons, too. The triggerfish’s body is designed to enable it to prey on these invertebrates in relative safety. Its head is long and tapering, with the easily damaged eyes set high up and well back from the mouth.

There are also powerful teeth in the triggerfish’s jaws. When feeding on sea urchins, triggerfish pick them up and drop them onto the seabed.Once the sea urchin lands upside down, the triggerfish can then rip away the shorter spines there, reaching the soft inside parts of its body.