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What is a Reef Triggerfish?

R. Britton
R. Britton

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.

Frog
Frog

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.

Frequently Asked Questions

What is a reef triggerfish and where can it be found?

The reef triggerfish, also known as the rectangular triggerfish or by its Hawaiian name 'humuhumunukunukuapua'a', is a tropical marine fish native to the Indo-Pacific region. It's commonly found in coral reefs where it feeds on algae, crustaceans, and small invertebrates. This species is particularly abundant around the Hawaiian Islands, where it's recognized as the state fish.

How does the reef triggerfish get its name?

The name "triggerfish" comes from its unique dorsal spines. The first spine, or 'trigger', can be locked upright and is used to wedge the fish securely into crevices, deterring predators. The second spine, which is smaller, 'triggers' the locking and unlocking of the first spine, hence the name 'triggerfish'.

What are the distinctive features of a reef triggerfish?

A reef triggerfish boasts a diamond-shaped, laterally compressed body with bold, geometric patterns. Its coloration is a mix of tan, yellow, and black, which provides camouflage among the coral. It has small, but strong jaws with teeth adapted for crushing shells, and its anterior dorsal fin is modified into the characteristic trigger spine.

What is the ecological role of the reef triggerfish in its habitat?

As a benthic feeder, the reef triggerfish plays a crucial role in controlling the population of bottom-dwelling invertebrates and algae in coral reef ecosystems. By consuming these organisms, it helps maintain the balance and health of the reef, which in turn supports biodiversity and provides a habitat for numerous marine species.

How does the reef triggerfish behave when threatened?

When threatened, the reef triggerfish uses its unique dorsal spine mechanism to lock itself into rock crevices, making it difficult for predators to extract it. Additionally, it can produce a grunting sound that may startle predators or communicate distress to other triggerfish, showcasing a fascinating aspect of its behavioral defense strategies.

Is the reef triggerfish important to local cultures or economies?

Yes, the reef triggerfish holds cultural significance, especially in Hawaii where it's the official state fish and a symbol of the local natural heritage. It's also a popular species in the aquarium trade due to its striking appearance and interesting behavior, contributing to local economies through sustainable fishing practices and ecotourism activities.

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