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The reef triggerfish, Rhinecanthus rectangulus, or humuhumu-nukunuku-apua'a, is a bottom-feeding marine fish found across a large geographic range. This species can be found around the outer edge of the world's tropical reefs. It is the state fish of Hawaii and has a variety of historical uses in Hawaii, including being the focus of ritual ceremonies. The reef triggerfish is also a popular marine aquarium fish.
This species reaches 1 foot (30 cm) and has a comparatively small mouth at the end of a large, tapering snout. The mouth of the reef triggerfish contains lots of needle-sharp teeth, situated very close together. The fish also has a powerful jaw, making it an efficient marine predator. Primary food sources include algae and other plant matter, crustaceans, sea urchins and mollusks, meaning the reef triggerfish is an omnivore. The wide, varied diet of this fish also incorporates small fish and marine invertebrates.
The reef triggerfish is rather unusual because it has the ability to move each eye in a different direction at the same time. One theory surmises that this allows the fish to search the sea floor for prey while simultaneously scanning for potential threats. Able to swim forwards and backward by undulating its dorsal and anal fins, the reef triggerfish is reasonably agile, able to out-maneuver both prey and predators. If threatened, the fish makes a deep grunting noise as it swims for safety.
Two spines are situated on top of the body just behind the head. The larger of the two spines can be raised and slopes backward. The smaller of the two spines slopes forward when raised, slotting under the larger spine. This creates a strong wedge-shape that the reef triggerfish uses to wedge tight into small gaps and crevices. Once wedged into place, this makes the fish incredibly difficult for predators to extract.
Although a popular marine aquarium species, the reef triggerfish can be very aggressive and territorial, so it is not advisable to keep more than one reef triggerfish per tank. In captivity, the fish should have plenty of places to hide and lots of open space in which to swim freely. The reef triggerfish will eat any other fish small enough to fit in its mouth and will also devour any marine invertebrates in the tank. The reef triggerfish is reasonably easy to keep in an aquarium setting — providing the tank is large enough and not too overcrowded — because they are hardy, not prone to disease and can tolerate changes in water condition.