Dusky Jawfish, Opistognathus whitehursti

Dusky Jawfish, Opistognathus whitehursti. Fish caught from coastal waters off Ft. Lauderdale, Florida, February 2022. Length: 9.8 cm (3.9 inches). Catch, photograph and identification courtesy of Ben Cantrell, Sebastian, Florida.

The Dusky Jawfish, Opistognathus whitehursti, is a member of the Jawfish or Opistognathidae Family, that is known in Mexico as bocón prieto. 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 Dusky Jawfish have an elongated compressed tapering body with a large bulbous head. Their head and body is densely mottled with dark brown and flecked with black. The upper back and head may have some white. They have a faint dark stripe overlaid by blotches along the mid-side, a dark bar between the eyes and a series of thin white bars on the top lip. The anal, caudal and dorsal fins are pale with rows of small brown spots or brown with rows of pale spots. They have a greenish-blue spot on the dorsal fin and the front of the dorsal fin. Their caudal fin and rear of their dorsal fin are yellow with rows of small black spots. Their eyes are large and set high on the head and their mouth is large and terminal that extends to the rear of the eyes and is equipped with 1 to 3 teeth on the roof and one row of teeth along the side of the top jaw. Their anal fin has 3 spines and 13 or 14 rays and a long base; their caudal fin is rounded; their dorsal fin has 11 spines and 14 or 15 rays and a long base; and, their pelvic fins are short and have 1 spine and 5 rays with the outer 2 being strong and branched and the inner 3 weaker and branched and occur before pectoral fins. They have 24 to 32 gill rakes. They are covered with smooth small scales which are absent from the head. Their lateral line is only on the front half of the body.

The Dusky Jawfish is found within rock and sandy substrate adjacent to reefs, residing in burrows which it enters tail first, at depths up to 60 m (200 feet). They reach a maximum of 14 cm (5.5 inches) in length. Unhatched fish are mouth brooded by the males and juveniles are guarded by both parents. Their larval stage is short, and the juveniles are prone to predation, including the invasive Red Lionfish, Pterois volitans, and they utilized burrowing to avoid predation. Dusky 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 Dusky Jawfish can be confused with the Banded Jawfish, Opistognathus macrognathus (white background, white top jaw with a black stripe) and the Mottled Jawfish, Opistognathus maxillosus. (double white blotch separated by brown at the base of the caudal fin).

The Dusky Jawfish is a resident of Mexican waters of the Atlantic Ocean being found from Tuxpan south within the coastal waters of the Gulf of Mexico and along the east coast of the Yucatán Peninsula in the Caribbean.

From a conservation perspective the Dusky Jawfish is currently considered to be of Least Concern, with stable, widely distributed populations. They are small in stature and of limited interest to most, however, they are utilized by the aquarium trade at a nominal level.