Abstract
Atresia in the ovaries of sardine Sardina pilchardus did not show clear seasonal patterns. There was high prevalance (c. 60%) and low intensity (c. 1% of gonadal area occupied by oocytes) in all months of the spawning season studied. The batch size to ovary-free mass relationship was significantly different in the mid-spawning season, with higher relative fecundity and gonadosomatic index (IG) in January than in November and March. There was no additional effect on batch fecundity due to age or condition factor. Data from monthly market samples during 1998–1999 revealed a continuous decline of the condition factor throughout the spawning season. The market samples also revealed that the duration of the spawning season is not equal for all fish. In any month, pre-spawning fish tended to have significantly higher IG than spawners, indicating that delayed initiation of spawning can lead to larger relative fecundity. The increase in sardine relative fecundity during the first half of the spawning season is probably due to the continuous influx of new spawners and possibly to body mass loss that is initially not translated into gonad mass loss. After January when all visible fat reserves within the body cavity have disappeared, the influx of new spawners practically ceases.
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