Spottail Pinfish, Diplodus holbrookii
The Spottail Pinfish, Diplodus holbrookii, whose common Spanish name is sargo cotonero, is a member of the Porgy or Sparidae Family, known collectively as plumas in Mexico. Globally, there are 14 species in the genus Diplodus, of which two are found in Mexican waters of the Atlantic.
The Spottail Pinfish have oval and compressed bodies with a depth that is 43% to 47% of standard length. Juveniles have five narrow vertical dark bars on their back and sides and an equal number of short intermediate bars on their back. Adults are steel blue dorsally and silvery on their sides; they have a large black spot just in front of their caudal peduncle that reaches the lower peduncle margin (a key to identification). The membranes of their gill covers are black. Their head has a pointed snout, a straight profile, and small eyes. They have a mid-sized terminal mouth that reaches the front margin of the eyes and is equipped with six well-developed incisiform teeth and three rows of lateral molariform teeth on each jaw. Their anal fin lacks spines but has 13 to 15 rays; their caudal fin is deeply forked; their dorsal fin has 12 or 13 spines and 13 to 16 rays; and their pectoral fins are long. They have 17 to 21 short gill rakers on their first arch. They are covered with smooth scales.
The Spottail Pinfish are a schooling species found in shallow seagrass flats, eelgrass beds, breakwaters, jetties, piers, wharf pilings, and areas of sparse vegetation on sandy or muddy bottoms at depths up to 250 feet. They reach a maximum length of 35 cm (14 inches) and weight of 1.2 kg (2.6 pounds). They are found mixed in with other species in water temperatures between 17.5oC (64oF) and 32.5oC (91oF) with high salinities and never in freshwater environments. Juveniles are normally found in shallow waters. They move to deeper waters around natural and artificial reefs and man-made platforms during warm water episodes and in winter as they mature. They are daytime feeders that consume plant materials and animals attached to plants including algae, plankton, copepods, small crabs, mollusks, small shrimp, as well as ectoparasites they obtain by cleaning other fish. They are a vital component of the marine ecosystem and are preyed upon by various barracuda, flatfish, groupers, porgies, seatrouts, snappers, and snooks. Reproduction is believed to occur via protandrous hermaphroditism. Fertilization is external with pelagic eggs and larvae. They have a lifespan of up to 11 years.
In Mexican waters, the Spottail Pinfish are limited to the western and southwestern Gulf of Mexico and normally found in deeper waters.
The Spottail Pinfish is most likely confused with the Silver Porgy, Diplodus argenteus (dark spot on caudal peduncle does not extend to peduncle margin).
The Spottail Pinfish are caught in abundance via hook and line, traps, seines, gill nets, and shrimp trawls but are normally a by-catch of other targeted fisheries. Although not pursued or sold commercially due to their small size, they are considered an excellent food fish and are retained by subsistence fishermen. They are used on a limited basis as live bait fish. From a conservation perspective, they are currently considered of Least Concern, being abundant with stable populations and a wide distribution.
Spottail Pinfish, Diplodus holbrookii. Fish caught from coastal waters off Tampa, FL, April 2011. Length: 20.0 cm (7.9 inches). Catch, photo, and identification courtesy of Ryan Crutchfield, Tampa, FL.