Testicular development and sperm morphology in the viviparous teleost, Zoarces elongatus
1993
Koya, Y. (Hokkaido Univ., Hakodate (Japan). Faculty of Fisheries) | Ohara, S. | Ikeuchi, T. | Adachi, S. | Matsubara, T. | Yamauchi, K.
The present study is on the testis structure, seasonal changes of germ cells, and morphology and motility of sperm in the viviparous teleost, Zoarces elogatus. In the testes of Z. elongatus, spermatogonia distributed throughout the seminal lobules, but most spermatogonia were located at the terminal end of the seminal lobule. This indicates that the testis of this fish is of the unrestricted spermatogonia type resembling the restricted spermatogonia type, typical of viviparous type fish. The annual change in the spermatogenesis of Z. elongatus was divided into five stages from a histological examination which is as follows: 1) Spermatogonial proliferation stage (November to December): Spermatogonia proliferate, and form spermatogonial cysts. 2) Early maturation stage (January to May): Spermatocyte and spermatid cysts appear in seminal lobules, showing the beginning of active spermatogenesis. 3) Late maturation stage (June to July): The number of spermatocyte cysts decrease and the number of spermatid cysts increase. Spermatids released from these cysts are found in the seminal lobule. 4) Functional maturation stage (August to September): Spermatids released into the lumen of seminal lobule complete spermiogenesis and the lumen of seminal lobules are filled with spermatozoa. Copulation appears to occur during this period. 5) Post-spawn stage (October): No spermatocyte is found in the seminal lobules. Residual spermatozoa remain in the sperm duct. The ultrastructural observation showed that the sperm of Z. elongatus have a discoidal head, six mitochondria and biflagellar tails. Morphological characteristics of the sperm did not differ from those of the oviparous species. The sperm was motile at isotonic condition, suggesting that the condition of the ovarian cavity of a mature female was suitable to retain the sperm motility of Z. elongatus
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