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

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.