Studies on the sexual maturation on the jack mackerel in the area close to Mar del Plata were carried out throughout the whole year, 56 almost ripe females between 160 and 210 mm in total length and between 38 and 78 g is weight were taken into consideration for fecundity determinations. The most importante results obtained during these studies are the following: The gonad index was rather high and reached the value of 11.5.-The reproduction season is a rather one and the spawning occurs mainly in December and January.-It is assumed that a female of this species spawns once over a reproduction season, but shedding numerous batches of eggs in short intervals.-The lowest value found for the fecundity was 15.825 ovocites and the highest one was 82.892.-It is started that there exist great differences in the fecundity between the females within the same size and weight groups. Publisher permission Published Perciformes, Carangidae, Trachurus lathami, surel, reproducción, fecundidad