Milt production by non-spermiating male Atlantic ž / salmon Salmo salar after injection of a commercial gonadotropin releasing hormone analog preparation, 17a-hydroxyprogesterone or 17a ,20b-dihydroxy-4-pregnen-3-one, alone or in combination

Ž . In three separate experiments, non-spermiating male Atlantic salmon Salmo salar were Ž . injected with a commercial salmon gonadotropin releasing hormone analog GnRHa preparation Ž . or vehicle propylene glycol . After 6 days, fish were also injected with 17a-hydroxyprogesterone Ž . Ž . 17P , 17a ,20b-dihydroxy-4-pregnen-3-one 17,20bP or vehicle. Injections were repeated on day 7, and after a further 24 h, milt was collected by catheterisation. Blood samples were also taken and both blood and seminal plasma were retained for analysis of steroid levels. Only those fish treated with GnRHa in combination with 17P displayed a consistent increase in milt volume Ž . relative to sham-injected controls approximately 2–4 fold whereas treatment with GnRHa alone, Ž . resulted in a significant increase in milt volume relative to controls approximately two fold on only one occasion. Treatment with GnRHa in combination with 17P tended to result in lower Ž . blood plasma levels of 11-ketotestosterone 11KT and higher levels of 17,20bP relative to other treatments. 11KT levels in blood and seminal plasma tended to be negatively correlated with 17,20bP levels. Treatment with GnRHa in combination with 17,20bP resulted in similar blood plasma steroid profiles as combined GnRHar17P treatment. Together, these results lend further support for the role of gonadal progestogens in mediating the processes that regulate milt volume ) Corresponding author. Tel.: q61-3-6289-3280; fax: q61-3-6289-3290. Ž . E-mail address: harry [email protected] H.R. King . – 0044-8486r01r$ see front matter q2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00472-5 ( ) H.R. King, G. YoungrAquaculture 193 2001 179–195 180 Ž . in fish, but may also suggest additional roles for gonadotropin GtH and 17P, indicating that spermiation may not be simply 17,20bP dependent. q 2001 Elsevier Science B.V. All rights reserved.