An intraannual analysis of intermediate fecundity, batch fecundity and oocyte size of ripening ovaries of Pacific sardine Sardinops sagax in northern Chile

抄録

An intra-annual analysis of the intermediate fecundity, batch fecundity and oocyte size of ripening ovaries of Pacific sardine (Sardinops sagax) in northern Chile was carried out over an annual cycle from April 1992 to March 1993. Both the shorter and larger oocyte size classes of ripening ovaries were used to estimate the intermediate fecundity and batch fecundity, respectively. The relationship between both fecundates and their respective mean oocyte sizes were studied as well. Clear seasonal variations of the intermediate and batch fecundity were observed, which follows a similar trend reported in previous studies for the reproductive cycle of S. sagax. Two peaks were found with two periods of lower production of oocytes between them: the first peak occurred around winter and the second around summer. Mean oocyte diameters of the intermediate mode (ODIM) and mean oocyte diameters of the most advanced mode (ODAM) were found to have the same seasonal traits; that is, bigger oocytes in winter than in summer. The highest decrease in the oocyte diameter occurred during those months with lower reproductive activity. Possible factors influencing the fecundity variations as reproductive season progressed are discussed.