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Seasonal fluctuation in the sexual maturity of the Japanese sardine



Seasonal fluctuation in the sexual maturity of the Japanese sardine



Bull Tdkai Reg Fish Res Lab 9: 151-171



Since April 1949 a systematic sampling of the Japanese sardine, Sardinops melanosticta from the commercial catch has been continuously conducted. Biologists have measured the gonad weight and the diameter of the largest ovum in every individual fish of samples taken along the entire coast of Japan. The authors examined geographical and seasonal changes of the diameter of. the largest ovum, and of the maturity coefficient (KG= Konadheight x 10*), of large-sized (body lengthy sardines taken in the three major fishing areas: northwestern waters off Kyushu, western part (along Yamaguchi to Fukui Prefectures) and northern part (Ishikawa to Aomori Prefectures) of the Japan Sea. Diameter of the ovum is generally related with the progress of maturity coefficient. For instance, the frequency of high maturity coefficient (over 11) increased remarkably among the fish with the maximum ovum larger than 0.8 mm in diameter. The following four common points of interests were found as to the maturity coefficient of fish taken in all the areas under study. i) Only about 4% of males and females had a low coefficient (below one). ii) The coefficient of males rarely exceeded 20; while that of females varied over a wide range with the maximum coefficient exceeding 50. iii) the frequency distribution of maturity coefficients of females was often polymodal. Among the modes, only one was usually noticeable at a coefficient lower than 14 (mostly lower than 10). The coefficients of males were usually distributed in a normal curve, iv) The modal coefficient of females was usually less than that of the males. The maximum maturity coefficient was observed for males and females during January and February in Kyushu, Feb. and March in the western Japan Sea, and late April and May in the northern Japan Sea. The coefficients during the above periods averaged 7-8, 8-10 and 9-12 in Kyushu, and the western and the northern Japan Sea, respectively. High coefficients (over 20) appeared only during January and February, and April and May, in Kyushu and the northern Japan Sea, but over a longer period in the western Japan Sea. The occurrence of high coefficient was later, and mean coefficient higher, in the northern area than the southern area. The maximum and modal values of the coefficients also increased from the southern area to the northern area. The geographical change was especially remarkable in females; in the southern two areas, only a few individuals were found with a coefficient over 40. Frequency distributions of maximum ovum diameter from large sardines sampled during the spawning season in the western Japan Sea and in Kyushu show two or three modes among fish, some of which had ova exceeding 0.8 mm. Even among the matured group, only a few individuals carried nearly ripe ova. It is concluded that usually many fish were not ready to discharge their ova even in the mid-spawning season. Ripe ovum occurred for a longer period in the western Japan Sea than in the northwestern waters off Kyushu.

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Accession: 023569312

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