Reproductive Endocrinology of Fishes

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Abstract
While evidence is currently lacking for the agnatha and elasmobranchs, the release of pituitary gonadotropin by the teleost pituitary appears to be under stimulatory control by the hypothalamus. Gonadotropin has to date only been purified from teleost pituitary glands. Bioassay and biochemical data suggest that the teleost pituitary gland elaborates only one gonadotropin; however, there is some conflicting histological data on this point. Salmon gonadotropin has a molecular weight of approximately 29,000 at neutral pH and approximately 13,000 at low pH or after treatment with 8m urea or 1m propionic acid. Radioimmunossays have recently been developed for carp and salmon gonadotropin. Immunological techniques have also been used to identify pituitary gonadotrops. Pharmacological treatment of fish with methallibure has permitted inhibition of gonadal development while treatment with clomiphene citrate has stimulated ovulation. The role of corticosteroids and other steroid hormones in ovulation is still not fully elucidated. It is possible that the control of ovulation may differ between species. Experiments are described which aim to enhance natural stocks of pink salmon by endocrine manipulation of sexual development in the male.

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