Involvement of gonadotrophin and steroid hormones in spermiation in the amago salmon, Oncorhynchus rhodurus, and goldfish, Carassius auratus

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Effects of intraperitoneal injections of chum salmon gonadotrophin (SGA) and various steroid hormones (17α,20β-dihydroxy-4-pregnen-3-one; 17α,20β-diOHprog, 17α-hydroxy-progesterone, testosterone, 11-ketotestosterone) on the induction of in vivo spermiation were examined in nonspermiating amago salmon ( Oncorhynchus rhodurus) and goldfish ( Carassius auratus). A single injection of SGA to amago salmon and two successive injections to goldfish induced strong spermiation responses. Similarly two successive injections of 17α, 20β-diOHprog caused precocious spermiation in both species; however, the response to 17α,20β-diOHprog was of lesser magnitude than that to SGA. The spermiation response of goldfish to 17α-hydroxyprogesterone was similar to that of 17α,20β-diOHprog. Neither testosterone nor 11-ketotestosterone were effective in inducing spermiation in amago salmon, but these steroids were found to be slightly effective in goldfish. Effects of a single injection of SGA on changes in serum levels of 17α,20β-diOHprog and 11-ketotestosterone were also examined in nonspermiating amago salmon. Serum levels of 17α,20β-diOHprog dramatically increased after treatment and peaked on Day 2 and thereafter declined quickly. Similarly, 11-ketotestosterone peaked on Day 2, but the levels remained high throughout the experimental period. Considered together, these findings are consistent with the suggestion that 17α,20β-diOHprog is involved in the process of spermiation in teleosts. It is further suggested that this hormone is a testicular steroidal mediator of gonadotrophin-induced spermiation in amago salmon.