海産無脊椎動物の生殖腺の成熟に関する研究-IV

Abstract

In order to elucidate the maturity and seasonal changes in the testes and the biological minimum size of the male tanner crab, Chionoecetes opilio (MAJIDAE, BRACHYURA), known as one of the most important products in the Japan Jea, the present examination was undertaken with emphasis on the histology. The materials used were caught by a motor trawl net which was operated in Wakasa Bay on the west coast of the Japanese mainland at a depth of 175-375m. In December, 1968, 45 specimens ranging from 36.8 (8 th molting stage) to 154.1mm in carapace width were examined to clarify the biological minimum size. On the other hand, 70 specimens collected from October to June, 1965 and again during the same period in 1966, were examined histologically to pursue their seasonal changes. With the exception of a few individuals, no mature spermatozoa were detected in any part of the seminiferous tubules in the specimens of the 8 th molting stage taken in December. The functional spermatozoa were detectable in the spesimens of the 9 th molting stage, and the anterior portion of the vas deferens was filled with many spermatophores. Seasonal changes in the testis of the adult animal was not so remarkable with regard to external appearance, weight or volume, coloration and histologic features. Almost all the stages of spermatogenesis, in particular the spermiogenesis, were found easily in the seminiferous tubules of specimens examined throughout the year, Similarly, a lot of spermatophores occurred in the anterior portion of the vas deferens throughout the year. These results indicat that the male crabs older than the 9 th molting stage and 49.2mm in carapase width may have the ability of reproduction and mate with females at any time.