The relationship between batch fecundity and egg size in Japanese sardine Sardinops melanostictus in Tosa Bay and off the Kii Channel, southwestern Japan from 1990 to 1993, was examined using females whose yolk volume of oocytes became constant after hydration at the final maturational stage. Positive correlations were recognized between these two among females whose batch fecundities were less than 30, 000 eggs, while negative correlations were recognized among females those of which were more than 30, 000 eggs, even if they were of the same body length or age. From 1990 to 1992, the former females distributed in the coastal area of Tosa Bay with relatively low surface temperature, while the latter females distributed in the offshore area of Tosa Bay or the frontal region of the Kuroshio Current off the Kii Channel with relatively high surface temperature. In 1993, these offshore spawners in the Kuroshio region became almost extinct, simultaneously many females that spawned more than 30, 000 eggs per single spawning were observed in Tosa Bay. These results suggest that the spatial changes of batch fecundity of sardines from 1990 to 1992, which influenced the egg size, resulted in the populationspecific fecundity.