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Picasso triggerfish (Rhinecanthus aculeatus). Not photographed in Hanauma Bay. Photographed by Adrian Pingstone in December 2005 and released to the public domain.


Triggerfish, also called Humu-Humus, are some of the most interesting and brightly colored fish in Hanauma Bay. They are easily recognized by their deep flat bodies, small pectoral fins and small eyes. Their eyes are placed high up on their head. They also have rough shaped scales that form a tough covering on their body.

Triggerfish have angular heads that protrude into snout-like noses. They have very strong jaws and small mouths with sharp teeth. In addition to their teeth, they can also protect themselves with small tail spines that can scratch and injure other fish or even humans. They are named triggerfish for these small “trigger like” spines. They have a top dorsal spike and another smaller spike on the bottom of the body.

They range in size from 14 to 16 inches, which make them some of the largest fish in the Hanauma Bay region. While snorkeling in Hanauma Bay, you may see many varieties of triggerfish. Your can distinguish them from other fish by their unusual body shape.

Their coloring varies depending on the type. For example, Titan triggerfish have highly visible yellow-orange scales, a bright orange tail and yellow markings on their face. Picasso triggerfish (in picture) are some of the most striking fish in Hanauma Bay. Their white body is contrasted with dark gray stripes, florescent blue accents and bright yellow eye markings.

Triggerfish Habits

Triggerfish are on the move constantly. While you are snorkeling, you will see them moving alone or in small groups around the reef. They do not slow down until nighttime when they use their lower spike to “trigger” into the sand for rest. They stick to the shallower areas of coral reef.

Triggerfish are some of the most aggressive fish in the reef. They can be very territorial, and this is especially true for nesting females. They make pig- grunting noises when disturbed or agitated. Aggressive behavior toward other fish is common. You may see them “bullying” other fish while you are snorkeling.

These fish are carnivores and they spend their days eating crabs, shrimp, sea urchins, worms and other invertebrates. They will also pick at clams and other animals attached to corals, which makes it look like they are eating from the coral. You may also see triggerfish eating other smaller fish. They do not hunt fish, but will opportunistically eat the flesh of dead fish.