Slingjaw Wrasse

The slingjaw wrasse (Epibulus insidiator) is a tropical fish species belonging to the wrasse family Labridae. It is commonly found in the Indo-Pacific region, specifically in coral reefs. While it is not a significant species for local commercial fisheries, it is often sought after in the aquarium trade. What may appear as a mundane fish at first glance, the slingjaw wrasse is distinctive due to its highly protrusible jaws.

Peter Simon Pallas originally described Epibulus insidiator as Sparus insidiator in 1770. In 1815, Georges Cuvier assigned it to its own monotypic genus, Epibulus. The genus now includes another species called Epibulus brevis, which was described in 2008. Therefore, E. insidiator is the type species for the genus Epibulus.

The specific name "insidiator" means "ambusher" or "lurker". Early naturalists believed that this species fed on terrestrial insects by spitting drops of water from its elongated mouth, hence the name.

The most striking feature of the slingjaw wrasse is its highly protrusible jaws. The mouth of this species can unfold into a tube that is almost half the length of its head. Male slingjaw wrasses have a greyish-brown color with orange on their back, a yellowish transverse bar on the flank, and a pale grey head marked with a thin black stripe through the eye. The scales of the male's body are edged with darker pigment. Females can either be bright yellow or dark brown, while juveniles are brown with thin white bars on their flanks and white lines radiating from their eyes. Some individuals have yellow blotches, a pale tail, and black pectoral fins. The dorsal fin typically has 9-10 spines and 9-11 soft rays, while the anal fin has 3 spines and 8-9 soft rays. The largest specimens can grow up to 54 centimeters (21 inches) in length. Another similar species, Epibulus brevis, has a smaller size, duller colored males, and females with black pigment on their pectoral fins, as well as longer pectoral fins.

The slingjaw wrasse possesses the most extreme jaw protrusion among fishes. It can extend its jaws up to 65% of the length of its head. This unique adaptation allows it to capture small fish and crustaceans. The genus Epibulus also possesses distinctive ligaments in its jaw structure, including the vomero-interopercular ligament, interoperculo-mandibular ligament, and premaxilla-maxilla ligament. These, along with changes to cranial bones, enable the extreme jaw protrusion.

The slingjaw wrasse can be found throughout the Indo-Pacific region, ranging from the eastern coast of Africa, 🇲🇬 Madagascar, and the 🌊 Red Sea to the 🌊 Indian Ocean coasts, islands, and the Pacific as far as Johnston Atoll in Hawaii. However, occasional individuals have been observed in the main Hawaiian chain. Their habitat extends north to 🇯🇵 Japan and south to 🇳🇨 New Caledonia (🇫🇷 Overseas France). Along the northern coasts of 🇦🇺 Australia, they can be found from the Houtman Abrolhos archipelago to reefs in the Coral Sea off Queensland.

This fish species inhabits coral-rich areas of lagoon and seaward reefs. Adults are commonly found along reef slopes or near drop-offs. The slingjaw wrasse feeds on small crustaceans living in coral and on other fishes. It is believed to be a protogynous hermaphrodite, where individuals start as females and may change to males as they grow. Male color intensity increases during courtship, characterized by collapsed caudal fins held upwards and folded anal fins stretched downwards. The intensity of male coloration can revert to normal when they feel threatened. Males establish territories, ranging from 500 to 1,000 square meters (5,400 to 10,800 square feet), and multiple females appear to have their own home ranges within the male's territory. Spawning occurs around high tide, with the pair ascending 2-3 meters (6.6-9.8 feet). Spawning events have been observed in various months, including March, April, May, July, September, and October. Interestingly, the slingjaw wrasse can change its color to mimic grazing 🇮🇳 Indian sailfin tangs (Zebrasoma desjardinii) when their territory is invaded. This allows the wrasse to blend in with the tangs and hide among them to hunt using similar movements. It becomes challenging to distinguish the mimicking slingjaw wrasse from the herbivorous tangs.

The slingjaw wrasse is harvested for both food and the aquarium trade in several parts of its range. However, in 🇬🇺 Guam, there is no significant decline in the average body size of the fish caught over the past two decades until 2008.