Mexican Jawfish, Opistognathus walkeri

Mexican Jawfish, Opistognathus walkeri. Fish caught from coastal waters at a depth of 330-feet off Point Palmilla, Baja California Sur, June 2016. Length: 13.8 cm (5.4 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

Mexican Jawfish, Opistognathus walkeri. Fish caught from coastal waters off Loreto, Baja California Sur,  June 2024.  Length 14.5 cm (5.7 inches).

The Mexican Jawfish, Opistognathus walkeri, is a member of the Jawfish or Opistognathidae Family, that is also known as the Longjaw Jawfish and in Mexico as bocón Mexicano. The Mexican Jawfish is very newly discovered, introduced to science in 2003. 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 Mexican Jawfish has a deep compressed body with a slightly elevated back. They have a yellowish-brown base transitioning to white ventrally. They have three blue stripes along the body with the middle being the widest and the most prominent. Their anal fins are darker on the outer half. Their dorsal fin is tan with five prominent bars. In males the median fins are darker than the body; in females the median fins are the same color as the body. The inner lining of the top jaw is black. Their head is large, with a short snout, eyes set high on the face, a very steep profile above the mouth, and no cirrus. The mouth opens in the front and is large with a very long upper jaw. In males, the mouth extends past the gill cover and in females ends at the gill covers and has a thin, flexible, curved and pointed extension, and has conical teeth set in rows on both jaws and two stout conical vomerine teeth. Their anal fin has 3 spines, 11 or 12 rays and is slightly behind mid-body; their caudal fin is rounded; their dorsal fin has 11 spines and 12 or 13 rays originating just behind the top of the gill openings and is of moderate height has a uniform profile, with the rays being slightly longer toward the rear; their pectoral fins have 19 or 20 rays; and, their pelvic fins have elongated second rays that reach the anal fin in males. They have 21 to 26 gill rakers on the lower limb of the first arch and 38 or 39 in total. Their sides and belly are fully scaled. Their lateral line is only present on the first half of the body and terminates below the second dorsal fin ray.

The Mexican Jawfish is found in sandy or rubble substrate burrows, which it enters tail first, at depths between 21 m (69 feet) and 90 meters (295 feet). They reach a maximum of 14.5 cm (5.7 inches) established by the fish photographed above. The juveniles are found in shallower waters than the adults. The Mexican 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 Mexican Jawfish is mostly likely confused with the Toothy Jawfish, Opistognathus brochus (black anal fin; caudal fin with two bars).

The Mexican Jawfish is a resident of Mexican waters of the Pacific but has a very limited distribution, documented historically only in the central western Sea of Cortez. The fish photographed above represents a significant range extension to the extreme southwestern section of the Sea of Cortez.

From a conservation perspective, the Mexican Jawfish is currently considered to be Data Deficient. They are small in stature, exceedingly rare and seldom seen by humans.