Whitemouth Jack, Uraspis helvola

Whitemouth Jack, Uraspis helvola. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, January 2010. Length: 27 cm (11 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

Whitemouth Jack, Uraspis helvola. Fish caught from coastal waters off Mazatlán, Sinaloa, April 2015. Length: 32 cm (13 inches). Catch and photograph courtesy of Jeff Dawson, Joseph, Oregon. A most unusual striped fish. Identification courtesy of Dr. Robert N. Lea, Monterey, California.

The Whitemouth Jack, Uraspis helvola, is a member of the Jack or Carangidae Family, and is known in Mexico as jurel lengua blanca. There are three global members of the genus Uraspis of which two found in Mexican waters, one in the Atlantic and one in the Pacific Ocean.

The Whitemouth Jack has an oblong moderately compressed body with a depth that is 37% to 41% of standard length. They are overall dusky silver in color with a lighter-colored belly. The roof and floor of their mouth are white (after which they are named) and the rest of their mouth is blue-black. Their head has a rounded snout and their mouth reaches under the front part of the eyes. Their anal fin has 2 isolated spines followed by 1 spine and 19 to 22 rays and has a long base; their caudal fin has a narrow base and is deeply forked; their first dorsal fin has 8 spines and is shaped as a small low triangle their second dorsal fin has 1 spine and 19 to 22 rays and has a long base and is slightly longer than the anal fin base; their pectoral fins are long and curve; and, their pelvic fins are short. They have 5 to 8 gill rakers on the top arch and 13 to 17 gill rakers on the lower arch. Their body is covered with oval scales.Their arched lateral line becomes very pronounced anteriorly and has 23 to 40 small scutes. They lack finlets behind their anal and dorsal fins.

The Whitemouth Jack is a coastal pelagic species found in small schools from the surf zone to depths up to 402 m (1,320 feet); they are occasionally collected in bottom trawls. They reach a maximum of 81 cm (2 feet 8 inches) in length. As of January 1, 2023, the International Game Fish Association world record stood at 0.5 kg (1 lb 2 oz) with the fish caught from coastal waters off Japan in August 2016. The Whitemouth Jack  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 Whitemouth Jack is circumglobal and found in most tropical and temperate seas. In Mexican waters they are virtually unknown with the fish photographed above documenting its presence in the coastal waters of the Pacific at least in the states of Baja California Sur and Sinaloa.

The Whitemouth Jack cannot be easily confused with any other species, due to the coloration of its mouth.

From a conservation perspective the Whitemouth Jack is currently considered to be of Least Concern with stable, widely distributed populations. In certain regions they are caught by subsistence fishermen utilizing hook and line, seines and traps. They are also caught at a modest level as a by-catch of trawls but are insignificant commercially.