Atlantic Thread Herring, Opisthonema oglinum
The Atlantic Thread Herring, Opisthonema oglinum, whose common Spanish name is sardina vivita de hebra, is a member of the Herring or Clupeidae Family, known collectively as sardinas in Mexico. Globally, there are only five species in the genus Opisthonema, four of which are found in Mexican waters, one in the Atlantic and three in the Pacific.
The Atlantic Thread Herrings have moderately deep, fusiform, and compressed bodies with a depth that is 34 to 38% of standard length. They are blue-green dorsally transitioning to silvery white on their sides and belly. They have a dark spot just behind the top corner of their gill cover. Some fish have dark longitudinal lines on their body. Their caudal fin has black tips and their dorsal fin margin and filament are dusky. Their head has a short oblique mouth that opens at the front and is equipped with small conical teeth. Their anal fin is short with 22 to 24 rays and located well behind the dorsal fin. Their caudal fin is forked. Their dorsal fin has 18 or 19 rays and is located before the center of the body; its last fin ray is long and filamentous and extends to the caudal fin base. Their pelvic fins are on the abdomen and inserted under the center of the dorsal fin base. They have 26 to 46 fine gill rakers and their belly has a distinct keel. They are covered with small irregular scales.
The Atlantic Thread Herrings are a small coastal pelagic species and are widely distributed, common, and locally abundant in large schools found on the surface. They can also be found at depths up to 600 feet but are normally seen in waters less than 10 feet deep. They reach a maximum length of 48 cm (19 inches). They consume zooplankton including copepods, small fish, crabs, and shrimps. They are an important forage fish for large predatory fish. They are exceptionally fast and agile and make inshore migrations for reproduction. Reproduction is oviparous with each female releasing between 13,000 and 67,000 eggs per annum that are fertilized externally. They are known to enter estuaries and rivers for use as nursery grounds. They have a lifespan of up to eight years.
In Mexican waters the Atlantic Thread Herrings are found in all waters of the Atlantic.
The Atlantic Thread Herrings are most likely confused with the Threadfin Shad, Dorosoma petenense (prominent black shoulder spot).
The Atlantic Thread Herrings are caught globally at a level of 25,000 tons per annum. In Mexican waters they are caught primarily by beach seines and gillnets in small coastal fisheries by artisanal fishermen at a level of approximately 5,000 tons per annum but these numbers have recently declined significantly due to overfishing. They are also caught by hook and line and by cast nets and as a by-catch of menhaden and shrimp fisheries by trawlers. They are used extensively by recreational anglers as bait fish. With the exception of United States waters, they are currently unregulated. Commercially they are used primarily for fish meal and fish oil. They are canned and processed on a limited basis for pet food and human consumption. From a conservation perspective they are currently listed as of Least Concern, being common over a wide range with stable populations.
Atlantic Thread Herring, Opisthonema oglinum. Fish caught off the Sanibel Island Pier, Sanibel Island, Florida, April 2011. Length: 20.0 cm (7.9 inches). Catch, photo, and identification courtesy of Kenneth Tse, Toronto, Canada.
Atlantic Thread Herring, Opisthonema oglinum. Fish caught from coastal waters off Placida, Florida, March 2017. Length: 20.0 cm (7.9 inches). Catch, photo, and identification courtesy of George Brinkman, Guelph, Ontario, Canada.