Whitemouth Jack

Whitemouth Jack, Uraspis helvola

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

The Whitemouth Jacks have oblong moderately compressed bodies 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 first dorsal fin is shaped as a small low triangle. Their anal and second dorsal fins have long bases with the second dorsal fin base being slightly longer than the anal fin base. They have long curved pectoral fins. Their caudal fin is “V” shaped. Their arched lateral line becomes very pronounced anteriorly and has 23 to 40 small scutes. They lack finlets behind their anal and dorsal fins. Their body is covered with oval scales.

The Whitemouth Jacks are a coastal pelagic species found in small schools from the surf zone to depths up to 1,320 feet; they are occasionally collected in bottom trawls. They reach a maximum length of 81 cm (32 inches). They are circumglobal and found in most tropical and temperate seas. The Whitemouth Jack are poorly studied and very little is known about the their behavioral patterns.

In Mexican waters the Whitemouth Jack are virtually unknown with the fish photographed below documenting a significant range extension and the presence of this species in the extreme southwest corner of Baja.

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

Whitemouth Jack, Uraspis helvola. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, January 2010. Length: 27 cm (10 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, CA.

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