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The control of cyclical changes in the testicular activity of the lake chub Couesius plumbeus (Agassiz) Ahsan, Syed Nazar

Abstract

The annual testicular cycle of a teleost the lake chub (Couesius plumbeus) from a north temperate latitude (51°N) has been studied by histological and histochemical methods with a planimetric evaluation of the different spermatogenetic stages. The annual cycle is divided into five different stages and the cyclical testicular changes have been correlated with changing environmental conditions. Lobule boundary cells, considered to be homologue of the Leydig cells of higher vertebrates, have been identified, and the changes in their secretory activity have been reported. Temperature is the major environmental factor controlling the testicular cycle. The pituitary gland, through its gonadotropin(s), mediates between environmental changes and developments in the testes. Higher temperatures (16°-22°C) promote spermiogenesis and spermiation, whereas low temperatures (5°-12°C) are more conducive to gonial proliferation and the initial phase of spermatogenesis. Hypophysectomy affects the mitotic ability of the spermatogonia, completely blocks their transformation into spermatocytes and suppresses the secretory activity of the lobule boundary cells. Replacement therapy with fish gonadotropin and mammalian LH restores spermatogenesis to a large extent and maximum response is elicited with whole fish pituitary extract. It is proposed that the fish pituitary gonadotropin is similar to mammalian LH and in this species mammalian FSH is physiologically inactive in the restoration of testicular activity. Since whole fish pituitary produces a maximum response it is suggested that factors such as TSH and STH have a probable synergistic role in the testicular maturation in Couesius plumbeus. Evidence is presented that a weak endogenous rhythm of activity is partly responsible for the timing of various testicular changes.

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