Changes in the growth of the Japanese sardine Sardinops melanostictus during a period of declining stock size was examined by using sardines sampled from 1990 to 1996 in Tosa Bay, south-western Japan, one of the main spawning grounds on the Pacific coast of Japan during February and March. The growth parameter k-values of the von Bertalanffy growth equation of female sardines were small in the 1987-1990 years classes, while the values for the 1991-1992 years classes were larger, which corresponded closely with the decrease in catch of the sardines in south-western Japan, suggesting that there are density-dependent effects on the growth of sardines in Tosa Bay. In contrast, the body length decreased since the 1993 years class, but the fatness of female sardines improved after 1993. Since 1994, many I year females with transparent eggs in the ovaries have been collected from Tosa Bay. It is speculated that good nutritional conditions of the 1993 year class led to maturation at an earlier age, and that the decrease of growth from the 1993 year class occurred due to the reduction of resources channeled to growth as a result of the maturation at I year.

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