ニジマス成熟に関する研究-II : 1年魚の精巣の発達について
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概要
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The maturation of the testis of the rainbow trout was studied using a one-year old fish as materials. The results obtained are summarized as follows; 1) Morphological changes in spermatogenesis have been divided into seven stages. 2) Based on the maturity factor, maturing fish may be distinguished from the immature in May, and the difference between the two groups of fish becomes clear in August: i. e., the maturity factor of the maturing fish was above 1, while that of the immature was below 0.1. Thereafter, the distinction between the two groups becomes more and more striking at this point, and no fish ranking in the intermediate group between the maturing and the immature was recognized (Text-fig. 1). The fish of maturing group held in their testes a small amount of spermatozoa by May, and the spermatozoa increase in amount day by day as the spawning season draws near. On the other hand, the testes of most of the immature ones contained spermatogonia alone throughout the year. 3) The testicular maturity of this species has been represented by the ratio of spermatozoa to total germ cells found within the testis. The testicular maturity differs greatly in seasonal changes from maturity factor. The former increases in value month by month during the pre-spawning season, and its value was 12 in August, 45 in September, 70 in October and 90 in November, and attained 100 in December. On the other hand, the maturity factor arrived at the maximum value by September, then it decreased gradually by December with the advance of maturation, followed by a fair decrease in the spawning season (Text-fig. 2). The decrease of the maturity factor during the pre-spawning season may be attributed to the changes in the quality of germ cells in the course of spermatogenesis, and that found in spawning season could be caused by the discharging of reproductive products. 4) The maturing group of fish apparently were larger in body length than the immature group, but the body length of the immature male ranged more widely than that of the female fish, and thus the minimum size of the mature male was obscure in the present study.
- 公益社団法人 日本水産学会の論文
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