A Seasonal Cycle in the Testis of the Spurdog, Squalus Acanthias, and the Sites of 3β-Hydroxysteroid Dehydrogenase Activity

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Abstract
The histology of the spurdog (Squalus acanthias L.) testis was observed through a complete annual cycle. The maximum sperm accumulation coincided with the breeding time as defined by the biennial female cycle. Degeneration of spermatogonia was observed following breeding. The band of degenerate germinal ampullae was identical to that described as occurring in Scyliorhinus canicula (L.) following pituitary ventral lobectomy. This suggested a resting phase in the production of a specific pituitary gonadotrophin lasting for about four months. All spermatocytes were transformed to spermatozoa within 12 months. 3β-Hydroxysteroid dehydrogenase activity was located in semen, in Sertoli cell cytoplasm and in the lumens of mature germinal ampullae. A possible seasonal change in this activity due to the migration of the degenerate band is suggested. Interstitial cells of Leydig could not be observed.INTRODUCTIONThe Scottish-Norwegian stock of the spurdog, Squalus acanthias L., sampled for this study, was shown by Holden (1965) to make an autumn breeding migration from the region of the Orkney and Shetland isles to the breeding areas in the Minch off north-west Scotland. During January and February those females carrying embryos at the end of their second year of development move inshore and liberate their young in shallow water. At this time the ovaries of these fish contain from three to fifteen eggs ready for ovulation (Holden & Meadows, 1964), and observations suggest that copulation, ovulation and the commencement of a further pregnancy follow almost immediately. Following copulation, the spermatozoa must reach the oviducal gland at the head of the oviduct in order that the eggs may be fertilized before they are enclosed by the candle membranes.

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