Deepbody Thread Herring, Opisthonema libertate
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, California.
The Deepbody Thread Herring, Opisthonema libertate, is a member of the Herring or Clupeidia Family, that is also known as the Pacific Thread Herring and in Mexico as sardina crinuda. There are five global members of the Opisthonema genus, of which four are found in Mexican waters, one in the Atlantic and three in the Pacific Ocean.
The Deepbody Thread Herring has a moderately deep compressed body with a depth that is 36% to 40% of standard length. The 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 has 12 to 13 rays and is shorter than the head and located well behind the dorsal fin; their dorsal fin has 13 to 21 rays and is located mid-body and has an elongated filamentous ray at its end that reaches past the caudal fin base; their pectoral fins are long and reach past the dorsal fin origin; and, their pelvic fins have 7 rays. They have 63 to 110 lower gill rakers in fish that are greater than 14 cm (5.5 inches) in length (a key to identification). Their body is covered with small scales.
The Deepbody Thread Herring is a small pelagic coastal schooling species found over sandy bottoms at depths up to 70 meters (230 feet). They reach a maximum of 30 cm (12 inches) in length and are virtually weightless. The Deepbody Thread Herring 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 Deepbody Thread Herring is a resident of all Mexican waters of the Pacific Ocean.
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; 41 to 69 gill rakers in adults), the Slender Thread Herring, Opisthonema bulleri (body depth 31-32% of standard length; 25-36 gill rakers in adults), and the Threadfin Shad, Dorosoma petenense (long anal tail base; ventral profile with strongly convex keel).
From a conservation perspective the Deepbody Thread Herring is currently considered to be of Least Concern with stable, widely distributed populations. They are collected by deep-water purse seines mixed in with the Middling Thread Herring, Opisthonema medirastre at levels of 50,000 to 1000,000 tons per year. They are sold commercially for human food consumption frozen through the majority of the major Mexican food markets throughout the country, used to make fish meal and fish oil.