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Triggerfish have tough skin and strong, small jaws with chisel-like teeth. Their eyes are placed about a third of the way back, near the top of their bodies. This may help the triggerfish scan for food along the ocean floor, and may reduce damage to the eyes while rooting around in the sand for food. The humuhumu feed on invertebrates with hard skeletal parts, like crabs, mollusks, and sea urchins, as well as algae. Some species of triggerfish also eat plankton. As they dig their food out of the sand, they sometimes are seen expelling clouds of silt or sand from their gills.
Triggerfish have unique defense mechanisms that keep them from becoming lunch for bigger fish. When being chased by a predator, the humuhumu will dart into a puka, or hole, in the reef, erect the first of two dorsal spines, and use the second spine (the trigger) to lock the first one in place. They can also extend their pelvic bone to wedge themselves in from the bottom. These mechanisms prevent the predator from being able to remove the triggerfish from the puka. Triggerfish will often use the same puka to sleep in at night. The ability for the humuhumu to swim forward or backward by undulating their dorsal (top) and anal (bottom) fins also improves its chance for escape. They can also use their tail for quick bursts of speed, but rely on the dorsal and anal fins for their primary source of locomotion.