Fish Identification Photos: Shortfin Scad, Decapterus macrosoma: The Shortfin Scad is a member of the Carangidae or Jack Family found in Mexican waters.

The Shortfin Scad is characterized by its “mackerel-like” appearance, long aerodynamic slender body, metallic blue back with silver below, pointed head, short pectoral fins, prominent arched lateral line, jagged dorsal fin, and a characteristic black blotch at the top of its gill cover.

The Shortfin Scad can be easily confused with the Mackerel Scad, Decapterus macarellus (which has a less ragged dorsal fin and less pronounced lateral line), the Mexican Scad, Decapterus muroadsi (one finlet behind the anal and dorsal fins, and a flank with a yellow stripe bordered above and below by a blue stripe), and the Pacific Jack Mackerel, Trachurus symmetricus (enlarged scute-like lateral line, long pectoral fins, and no black spot on its gill covers).

The Shortfin Scad is pelagic and found in all Mexican waters south of Magdalena Bay, including throughout the Sea of Cortez, and along mainland Mexico through to Guatemala.

It is found at all depths of the water column, and is reported to reach a length of 14 inches. The Shortfin Scad utilized by locals as dead "decoy" that is trolled slowly behind the boat, sent "down-deep," or for cut bait.

Shortfin Scad, Decapterus macrosoma: Shows up when one purchases a “scoop of bait.” Caught on very rare occasions in the surf zone, La Playita, San Jose del Cabo, Baja California Sur, Mexico, during the winter months, with water temperatures below 75 degrees, early morning, in 5 to 10-foot deep water, utilizing a cast net thrown by panguero bait salesmen. Size 7 inches, and virtually weightless. Utilized by as a “dead decoy,” slowly trolled in the wake of the boat to attracted Dorado, et. al. Does not survive in a panga “bait tank” at a high level. Fish identification courtesy of Dr. Ross Robertson, Smithsonian Institute, Panama. Description and photo courtesy John Snow.