Giant Jawfish, Opistognathus rhomaleus
Giant Jawfish, Opistognathus rhomaleus, juvenile. Fish caught from coastal waters off Point Palmilla, Baja California Sur, September 2018. Length: 16.1 cm (6.3 inches).
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 lbs 3 oz and has been submitted to the IFGA for a new world record. Catch, photograph, and identification courtesy of Chris Wheaton, Fullerton, California.
Giant Jawfish, Opistognathus rhomaleus. Fish caught from coastal waters north of La Playita, Baja California Sur, March 2021. Catch and photograph courtesy of James Rosenwald, Saint Croix, Minnesota. This fish was was not measured but appears to be well in excess of the known maximum of the Giant Jawfish.
The Giant Jawfish, Opistognathus rhomaleus, is a member of the Jawfish or Opistognathidae Family, that is also known as the “Big Mouth Bastard” and in Mexico as bocón gigante. Globally, there are forty-three species in the genus Opistognathus, of which thirteen are found in Mexican waters, six in the Atlantic and seven in the Pacific Ocean.
The Giant Jawfish has a moderately elongated and tapering body. They are light gray or brownish in color with numerous small dark spots covering their head, upper back, and dorsal fin base. The pectoral fins are tan and their pelvic fins are black. Juveniles have five or six bars on their sides; adults do not. Their head is enlarged and bulbous, with a large tan mouth that extends past the eyes and is equipped with two to four teeth on the front roof of the mouth, and very large eyes found high on the head. Their anal fin has 2 spines and 13 rays and a long base; their caudal fin is short and rounded; their dorsal fin has 1 spines and 12 to 14 rays and a long base; their pectoral fins have 20 or 21 rays and are short; and, their pelvic fins have 1 spine and 5 rays and are located before the pectoral fins. Their bodies are covered with smooth scales. Their lateral line is high on the body and ends under the middle of the dorsal fin.
The Giant Jawfish live in shallow coastal waters on sandy or rubble substrate adjacent to coral or rocky reefs at depths up to 566 m (200 feet), however they avoid the surge zone. They reach a maximum of 51 cm (20 inches) in length and 1.8 kg (3 lbs 14 oz) in weight. As of January 1, 2024, the International Game Fish Association world record stood at 1.13 kg (2 lbs 8 oz) with the fish caught by my friends Chris Wheaton from within Bahia de Los Angeles, Baja California in December 2015. 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. They are generally found in colonies and feed primarily on benthic and planktonic invertebrates. They exhibit the unusual habit of oral egg incubation. The Giant Jawfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Giant Jawfish is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Magdalena Bay, Baja California Sur, 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).
From a conservation perspective the Giant Jawfish is currently consider to be of Least Concern with stable, widely distributed populations. They are very common in the greater Los Cabos area. They are of limited interest to most and are normally a “catch and release,” however they are retained by subsistence fisherman.