Deepbody Thread Herring, Opisthonema libertate
The Deepbody Thread Herring, Opisthonema libertate, whose common Spanish name is sardina crinuda, is a member of the Herring or Clupeidia Family known collectively as sardinas in Mexico. There are only five global members of the Opisthonema genus, four of which are found in Mexican waters, one in the Atlantic and three in the Pacific.
The Deepbody Thread Herrings have moderately deep compressed bodies with a depth that is 36 to 40% of standard length; adults have deeper bodies than juveniles. They are gray-green dorsally and silvery with narrow stripes and scattered black spots on their sides. They have a black spot just behind their gill covers. The inner portions of their anal and dorsal fins are pale yellow and the outer halves are clear. They have a short oblique mouth that opens at the front. Their anal fin base is shorter than the head and located well behind the dorsal fin. Their dorsal fin is located mid-body and has an elongated filamentous ray at its end that reaches past the caudal fin base. They have long pectoral fins that reach past the dorsal fin origin and 63 to 110 lower gill rakers (a key to identification). Their body is covered with small scales.
The Deepbody Thread Herrings are a small pelagic coastal schooling species found over sandy bottoms at depths up to 70 meters (230 feet). They reach a maximum length of 30 cm (12 inches) and are virtually weightless. They are a poorly studied species and very little is known about their behavioral patterns.
In Mexican waters the Deepbody Thread Herrings are found in all waters of the Pacific.
The Deepbody Thread Herring can be easily confused with the Middling Thread Herring, Opisthonema medirastre (body depth 30-36% of standard length; pectoral fin does not reach dorsal origin), the Slender Thread Herring, Opisthonema bulleri (body depth 31- 32% of standard length; 25 to 36 gill rakers), and the Threadfin Shad, Dorosoma petenense (long anal tail base; ventral profile with strongly convex keel).
The Deepbody Thread Herrings are too rare to be of interest to most. They are collected by deep-water sardine trawlers and sold commercially through the majority of the major Mexican food marketes country wide.
Deepbody Thread Herring, Opisthonema libertate. Commercial fish courtesy of Soriana’s Mercardo, Cabo San Lucas, Baja California Sur, July 2008. Length: 14 cm (5.5 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, CA.