Blackfin Jack, Hemicaranx zelotes

Blackfin Jack, Hemicaranx zelotes. Fish caught from coastal waters of Magdalena Bay, Baja California Sur, May 2017. Length: 27 cm (11 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institute of Oceanography, La Jolla, California.

Blackfin Jack, Hemicaranx zelotes. Fish caught from coastal waters of Magdalena Bay, Baja California Sur, August 2017. Length: 27 cm (11 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institute of Oceanography, La Jolla, California.

Blackfin Jack, Hemicaranx zelotes. Three fish caught from coastal waters of the greater Los Cabos area of Baja California Sur, December 2019. Length: ca. 41 cm (16 inches). Catch courtesy of Les and Connie Bezeredi, San José del Cabo, Baja California Sur. Fish staged by Brain Brictson and photographs courtesy of Eric Brictson, Gordo Banks Pangas, La Playita, Baja California Sur. Identification courtesy of H.J. Walker, Jr., Scripps Institute of Oceanography, La Jolla, California. Note: these fish are significant bigger than the known maximum length for the Blackfin Jack.

Blackfin Jack, Hemicaranx zelotes.  Underwater photograph taken in coastal waters off Puerto Vallarta, Jalisco, July 2023. Photograph courtesy of Kevin Erwin, Seattle, Washington.

The Blackfin Jack, Hemicaranx zelotes, is a member of the Jack or Carangidae Family, and is known in Mexico as jurelito chocho. Globally, there are four species in the genus Hemicaranx, all of which found in Mexican waters, two in the Atlantic and two in the Pacific Ocean.

The Blackfin Jack has a “jack-like”, moderately compressed, oval, and fusiform body with a depth that is 35% to 39% of standard length. They are silvery blue dorsally and transition to silvery white ventrally. Juveniles have four or five bars on their sides. Their head and snout are black. They have a large black area on their pectoral fin axis. Their fins are dark. Their head is small with a blunt rounded snout. They have a small mouth with a slightly projecting lower jaw that does not reach their moderately large eyes. They are equipped with a single series of small close-set teeth on each jaw. Their anal fin has 1 spine and 22 to 25 rays; their caudal fin has a slender base and is wide and forked with a longer upper lobe; their first dorsal is preceded by an antrose spine, has 7 or 8 spines and is low; their second dorsal fin has 1 spine and 25 to 31 rays and is similar to the anal fin; and, their pectoral fins are long and reach the anal fin origin. They have 7 to 10 gill rakers on the lower arch and 18 to 23 gill rakers on the upper arch. Their body is covered with small scales. Their lateral line is strong with a short and pronounced high anterior arch with 47 to 55 strong well developed scutes.

The Blackfin Jack is a benthopelagic schooling species found in coastal waters at depths up to 30 m (100 feet). They are known to enter brackish waters. They reach a maximum of 35 cm (14 inches) in length. They are opportunistic predators and feed on benthic and pelagic fish as well as squid and crustaceans. The Blackfin 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 Blackfin Jack is a resident of Mexican waters of the Pacific but has a limited range being found from Magdalena Bay, Baja California Sur, southward along the southwest coast of Baja, in the lower half of the Sea of Cortez, and southward along the coast of the mainland to Guatemala.

The Blackfin Jack can be confused with the Whitemouth Jack, Uraspis helvola (oblong body; inside of mouth white) and the Yellowfin Jack, Hemicaranx leucurus (yellow fins).

From a conservation perspective the Blackfin Jack is considered to be of Least Concern with stable, widely distributed populations. They are of minor commercial importance being caught as a by-catch by shrimp trawlers and in gill nets and marketed fresh and salted or dried on a limited basis.