Effect of maintenance at elevated temperatures on ovulation and luteinizing hormone releasing hormone analogue responsiveness of female Atlantic salmon (
Salmo salar) in Tasmania
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King, HR and Pankhurst, NW, Effect of maintenance at elevated temperatures on ovulation and luteinizing hormone releasing hormone analogue responsiveness of female Atlantic salmon (
Salmo salar) in Tasmania, Aquaculture , 233, (1-4) pp. 583-597. ISSN 0044-8486 (2004) [Refereed Article]
To examine the effect of maintenance at elevated water temperatures on the responsiveness of female Atlantic salmon (Salmo salar) to luteinizing hormone releasing hormone analogues (LHRHa), sexually maturing 2-year-old female Atlantic salmon were maintained at water temperatures of 6, 11 or 16°C from late in vitellogenesis (early April in Tasmania) throughout the periovulatory period (late April to early June). In early May, fish were treated with LHRHa (25 μg kg-1 body weight) by injection or in a cholesterol pellet. Controls received saline injections and blank pellets. Fish were anaesthetised and blood sampled at treatment, and at 48-h intervals for up to 8 days post injection. Thereafter, regular ovulation checks were conducted until the end of the experiment. Plasma levels of the gonadal steroids testosterone (T), 17β-estradiol (E2) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured and egg fertility and survival to the eyed stage were assessed. In controls, maintenance at 11°C delayed ovulation relative to fish held at 6°C whereas, in fish held at 16°C, ovulation was inhibited until holding temperature was reduced to 8°C on day 35 post injection. Treatment with LHRHa advanced ovulation in fish held at both 6 and 11°C but had no effect on ovulation in fish held at 16°C. Elevated plasma 17,20βP in controls was only evident in those fish held at 6°C (>100 ng ml-1), whereas LHRHa treatment was associated with high 17,20βP levels in fish held at both 6 and 11°C (>60 ng ml -1). In contrast, there was little production of 17,20βP in fish held at 16°C irrespective of treatment (<25 ng ml-1). In controls, prior maintenance at 16°C was associated with significant reductions in the fertility and survival of ova (84.0% and 17.3%, respectively) relative to 6°C (97.9% and 75.6%, respectively) and 11°C (95.3% and 44.4%, respectively). The fertility and survival of ova from LHRHa-treated fish held at 6 and 11°C did not differ significantly from that of controls but LHRHa-treated fish held at 16°C either produced nonviable ova or died prior to ovulation. These observations indicate endocrine dysfunction and confirm a lack of maturational competence in Atlantic salmon maintained at elevated temperatures, and suggest that both impaired pituitary responsiveness and limited 20β-HSD activity may contribute to the observed lack of 17,20βP production in fish held at 16°C. © 2004 Elsevier B.V. All rights reserved.
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