The humphead parrotfish, giant parrotfish, or humphead wrasse (Bolbometopon muricatum) is the largest species in the parrotfish family, reaching up to 1.3 meters in length and nearly 50 kilograms in weight. These curious fish can be found in the reefs of the Indian and Pacific Oceans, the Red Sea, the Great Barrier Reef of Australia, and some areas within The Coral Triangle.
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Its vertically profiled head is unique among parrotfish and is uniformly covered in scales, except for the forehead, which is often light green to pink. Juveniles are gray with scattered white spots, and as they mature, the gray turns into dark green. When they reach maturity, they develop their characteristic bulbous forehead, and, like other parrotfish species, they have very robust teeth that protrude from the mouth. The growth of this fish is slow, and they typically live up to 40 years. They are a gregarious species and are usually found in small groups, but occasionally the group size can be quite large, up to 75 individuals.
Giant parrotfish are highly gregarious and are typically found in groups. Image by _Bunn
These parrotfish live in reefs at depths of up to 30 meters where they feed on live hard corals, smashing them with their foreheads to break them down for easier consumption, and they don't hesitate to use their powerful dentition to dislodge rocks to reach the most nutritious corals. Each adult fish ingests over 5 tons of structural reef carbonates per year, significantly contributing to reef erosion. However, their coral sand excretions aid in creating new reefs and amazing tropical beaches of fine sand.
A special characteristic of these fish is that at night, if there are shipwrecks in their living area, they tend to venture into them to seek shelter, and it is common to find groups of giant parrotfish resting. This circumstance occurs, for example, at the Liberty shipwreck in Bali, where there are resident groups of these fish. It is a species classified as "vulnerable" by the IUCN due to habitat destruction and commercial fishing, taking advantage of the gatherings of these fish, especially at night, for easier fishing, as well as sport fishing.
Recently, a group of marine biologists observed a curious behavior never before seen. Investigating schools of giant parrotfish in the Wake Atoll, they heard loud noises caused by the violent head impacts of the largest males in the group. These large fish used their caudal fins to strongly bash their heads to demonstrate, as many caprid species do on land, strength and superiority over their contenders. It was even observed that, as the losing male fled, the dominant male attempted to bite the loser's fin.
The reason this behavior had never been seen before, according to these NOAA scientists, is that the giant parrotfish population is declining and now they have to compete for the right to reproduce.