Control of sex inversion in female Atlantic salmon (Salmo salar)

Commercial production of Atlantic salmon, Salmo solar (L.), in Tasmania is becoming increasingly reliant on female stocks for year round production. Hatchery production of female monosex stocks uses milt from sex inverted females (
eomales\") to produce all female offspring. This study was undertaken investigate the effects of aromatase inhibitors (Al) on Atlantic salmon and to facilitate the development of techniques for their commercial application. Dietary treatment for 800 ¬¨‚àûC days from first feeding with methyltestosterone at doses of 1 or 3 mg kg\\(^{-1}\\) food or methyldihydrotestosterone (MDHT) at 1 mg kg\\(^{-1}\\) food resulted in 100% masculinisation of female Atlantic salmon. Masculinisation followed 2 h immersion of alevins in MDHT at 400 ˜í¬¿g\\(^{-1}\\) during the period 0 to 28 days post median hatch (DPMH) and complete masculinisation was achieved after immersion at 14 and 21 or 14 and 28 DPMH. More sex inverted males with patent sperm ducts were produced by immersion than dietary treatments. The capacity of five AI: 146-androstatriene-317-dione (ATD); 4-androstene-4- ol-317-dione (OHA); 1424-dich1oro-˜í‚â§-([24-dichlorobenzyl]oxy)- phenethyl]imidazole (miconazole); 3[p-aminopheny1]-3-ethyl-piperidine-26- dione (aminoglutethimide) and 445678-tetra-hydroimidazo-(15-˜í¬±)-pyridin-5- yl] benzonitrile monohydrochloride (fadrozole) to reduce estradiol (E\\(_2\\)) production by Atlantic salmon brain and gonadal tissue was assessed in vitro. Fadrozole was the most potent effective at doses of 0.1-10.0 ˜í¬¿g ml\\(^{-1}\\). ATD OHA and miconazole were also effective on brain and gonadal tissue but aminoglutethimide was only effective on brain tissue. Immersion of Atlantic salmon alevins in ATD at a dose of 0.5 mg L\\(^{-1}\\) on 14 or 14 and 28 DPMH produced 13% neomales. This incidence was increased to 47 and 22% following treatment on 7 and 14 or 14 and 21 DPMH respectively and to 51- 54% with a dose of 5 mg \\(^{-1}\\) ATD. Miconazole aminoglutethimide fadrozole and OHA were all ineffective for sex inversion. Precocious maturation was induced by photoperiod manipulation and 67-88 % of mature neomales had patent sperm ducts and fertility (~70%) comparable to normal males. ATD was taken up by alevins more readily than OHA; however tissue levels of both declined by 50% after 24 h and by >90% after 7 days. Uptake levels declined with alevin age but retention rates were similar. Reducing the inter-treatment interval to 7 days resulted in increased androgen levels following the second treatment with ATD. Immersion in fadrozole at doses of 10 and 50 mg L\\(^{-1}\\) resulted in tissue levels of 300 and 1000 ng fish\\(^{-1}\\) which declined by 80% after 3 days. These studies demonstrate the commercial feasibility of androgens and AT for sex inversion of Atlantic salmon. The efficacy of immersion treatment with AT is dependent on both enzyme inhibition and the uptake and retention characteristics of AI."