The green humphead undefined, scientifically known as Bolbometopon muricatum, is the largest species of undefined, reaching lengths of up to 1.5 meters (4.9 feet) and weighing as much as 75 kilograms (165 pounds). This impressive fish inhabits coral reefs in both the 🇮🇳 Indian and 🌊 Pacific Oceans, from the 🌊 Red Sea to 🇼🇸 Samoa, and as far north as the Yaeyama Islands in 🇯🇵 Japan to the Great Barrier Reef in 🇦🇺 Australia, living at depths ranging from 1 to 40 meters.
Known by various common names—such as bumphead, humphead, double-headed, buffalo, and giant undefined—this species is unique because it is the sole member of its genus, Bolbometopon. Notably, it is the largest herbivorous fish residing in coral reef ecosystems.
Visually distinct, the green humphead undefined stands out with a vertical head profile and a body uniformly covered in scales, except for the leading edge of the head that showcases shades of light green to pink. It lacks the striking color changes seen in some other undefined species. Initially, the fish exhibits a dull gray color with scattered white spots, gradually turning a rich dark green as it matures. Adults are characterized by a prominent bulbous forehead and partially exposed teeth plates due to their large lips.
This species has a slow growth rate and can live up to 40 years. Its life cycle is unique in that both sexes look similar throughout their lives. Green humphead undefined reproduce by spawning near the outer edges of reefs or in specific spots during a lunar cycle, typically just before the new moon.
Juvenile undefined begin life in sheltered lagoons amidst branching coral habitats, often interacting with damselfish. As they grow, they move to lagoons, frequently associating with seagrass beds, before eventually venturing to the more open water of outer lagoons and seaward reefs as adults, up to 30 meters deep. Their diet consists of benthic algae and live corals, and they are known for headbutting corals to aid in feeding. This feeding behavior results in the ingestion of over five tons of reef carbonates annually by each adult fish, playing a significant role in the natural erosion of coral reefs. At night, these fish rest among corals, caves, and even shipwrecks, often in large groups.
The green humphead undefined is a victim of its own characteristics: large size, slow growth, and schooling behavior make it highly susceptible to overfishing. Fishermen often target these fish, particularly as they sleep, leading to a noticeable decline in their numbers. The species was marked as a Species of Concern by NOAA/NMFS in 2004 due to the lack of sufficient data for Endangered Species listing, highlighting the pressures from overharvesting and habitat deterioration. Poor water quality, often resulting from sediment runoff due to deforestation, further threatens their juvenile habitats.
Several protective measures have been implemented to safeguard this species. Spearfishing while scuba diving was prohibited in American 🇼🇸 Samoa in 2001, and specific marine areas around Wake Island, Johnston Atoll, and Palmyra Atoll are designated as protected zones, requiring special permits for fishing. Further restrictions include a ban on nighttime spearfishing with SCUBA gear in these regions. In Palau, conservation efforts have been bolstered by enforcing an export ban to help stabilize the undefined population. These measures aim to address the decline and ensure the survival of the green humphead undefined for future generations.
Why it's threatened
Threat classification from the IUCN Red List.
