Distribution, abundance and reproduction of Opisthonema oglinum (Pisces : Clupeidae) in the continental shelf, southern Gulf of Mexico

At present the ecological understanding and evaluation of tropical demersal fish communities have their bases on studies about the biology and ecology of dominant species. The Campeche Sound, in the southern Gulf of Mexico, h as more than 300 species in the demersal fish community and 30 are dominant s. Among these species, Opisthonema oglinum is dominant by its frequency, d istribution and abundance. This work determined the pattern of abundance an d distribution of O. oglinum, and its reproduction. maturity and recruitmen t. Fish were collected with a shrimp trawl net during six oceanographic cru ises in the Campeche Sound. The cruises correspond with the three character istic seasons in the area: rainy, "nortes", and dry season. A total of 813 individuals with sizes between 56 and 205 mm of total length were collected ; they weighted 30 211.5 g. O. oglinum is a typical pelagic-neritic species , and is estuarine dependent. This species occurs in the inner shelf waters of the Campeche Sound, less than 36 m deep and mainly in areas influenced by coastal discharges. It also occurs in the Terminos Lagoon (southern Camp eche Sound) and occasionally in the riverine systems that drain into the la goon. The highest biomass and density are on depths lesser than 20 m, in Ju ne and August-October. The high density of juveniles mainly determines the higher biomass. Maturity can start at a total length of 126 mm, but the siz e of first maturity is 135 mm of total length. Reproduction occurs from May to October with two evident peaks during May and August in depths greater than 18 m. The juveniles are found in the shelf and inside of the Terminos Lagoon. Recruitment is from June to October (rainy season). The visceral an d gonadic indices showed that the greatest alimentary activity is from June to August and in November. The condition factor is lowest in June, where t he recruitment is highest, and highest in November, after spawning.