Giant Jawfish

Giant Jawfish, Opistognathus rhomaleus

The Giant Jawfish, Opistognathus rhomaleus, whose common Spanish name is bocón gigante and also has been given the name “Big Mouth Bastard”, is a species in the Jawfish or Opistognathidae Family, known as collectively bocónes in Mexico. Globally, there are forty-three species in the genus Opistognathus, thirteen of which are found in Mexican waters, six in the Atlantic and seven in the Pacific.

The Giant Jawfish have moderately elongated and tapering bodies. They are light gray or brownish in color with numerous small dark spots covering their head, upper back, and dorsal fin base. The pelvic fins are black. Juveniles have five to six bars on their sides; adults are without these markings. Their head is enlarged and bulbous, with a large tan mouth that extends past the eyes and is equipped with two to 4 teeth on the front roof of the mouth, and very large eyes found high on the head. Their anal and dorsal fin bases are long; their caudal fin is short and rounded; the dorsal fin is continuous; the pectoral fins are tan and large; and, the pelvic fins are located before the pectoral fins and have one spine and 5 segmented rays. The lateral line is high on the body and ends under the middle of the dorsal fin. Their bodies are covered with smooth scales.

The Giant Jawfish live in shallow coastal waters on sandy or rubble substrate adjacent to coral or rocky reefs at depths up to 200 feet, however they avoid the surge zone. They reach a maximum length of 51 cm (20 inches), and 3.9 pounds in weight based on a fish caught in Bahia de Los Angeles in November 2017. They live in elaborate burrows that are self-constructed by utilizing their mouths and powerful jaws to excavate sand, small stones, and medium-sized rocks. Their burrows are frequently lined and reinforced with pebbles and shell fragments. The Giant Jawfish are generally found in colonies and feed primarily on benthic and planktonic invertebrates. They exhibit the unusual habit of oral egg incubation.

In Mexican waters the Giant Jawfish have a limited distribution being found from Magdalena Bay southward along the southwest coast of Baja, in the southern 80% of the Sea of Cortez, and along the coast of the mainland south to Guatemala.

The Giant Jawfish can be confused with the Finespotted Jawfish, Opistognathus punctatus (small spots covering the entire body, large eyes, yellow-orange color inside the mouth).

The Giant Jawfish are very common in the greater Los Cabos area. They are of limited value except to subsistence fisherman and are normally considered a “catch and release.”

Giant JawfishGiant Jawfish

Giant Jawfish, Opistognathus rhomaleus. Fish caught from coastal waters off Point Palmilla, Baja California Sur, May 2014. Length: 25 cm (9.8 inches).

Giant Jawfish, Opistognathus rhomaleus. Fish caught from coastal waters off Loreto, Baja California Sur, May 2017. Length: 48 cm (19 inches).

Giant Jawfish, Opistognathus rhomaleus. Fish caught from coastal waters within Bahia de Los Angeles, Baja California, November 2017. This catch documents a significant range extension for the species into the northern Sea of Cortez. Length: 48 cm (19 inches). Weight: 3.2 pounds and has been submitted to the IFGA for a new world record. Catch, photo, and identification courtesy of Chris Wheaton, Fullerton, CA.