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Testing the synergistic effects of GnRH and testosterone on the reproductive physiology of pre-adult pink salmon Oncorhynchus gorbuscha

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To test the hypothesis that the hypothalmic gonadotropin-releasing hormone (GnRH) and testosterone (T) co-treatment stimulates both the hypothalmo–pituitary–gonadal (HPG) and hypothalmo–pituitary–interrenal axes, the reproductive and osmoregulatory responses of pre-adult pink salmon Oncorhynchus gorbuscha were compared after GnRH and T administration either alone or in combination. Relative to controls, neither GnRH nor T treatment resulted in significantly greater ovarian or testicular growth, but co-treatment significantly increased ovarian growth after 5 months. Interestingly, the stimulation was undetectable after 3 months. However, once daily photoperiod began shortening after the summer solstice, c. 2 months before the natural spawning date, GnRH+T-treated females were stimulated to produce larger ovaries. Final fish body length and the size of individual eggs did not differ among treatment groups. GnRH+T eggs, however, showed signs of advanced vitellogenesis relative to GnRH-treated and control eggs, whereas T-treated eggs became atretic. Testis size increased significantly from initial values and most males were spermiating, but this growth and development were independent of hormone treatments. Final plasma ion, metabolite and cortisol concentrations did not differ among treatment groups. It is concluded that GnRH+T co-treatment was effective in stimulating female but not male maturation. GnRH and T treatment, however, presumably had little effect on the hypothalmo–pituitary–interrenal axis as observed by ionoregulatory status.

Keywords: cortisol; gonado-somatic index; maturation; ovarian development; photoperiod; reproductive hormones

Document Type: Editorial


Affiliations: 1: Centre for Applied Conservation Research and Department of Forest Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada 2: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON, K1S 5B6 Canada 3: Fisheries and Oceans Canada, Cooperative Resource Management Institute, Simon Fraser University, Burnaby, BC, V5A 1S6 Canada 4: Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2 W1 Canada 5: Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 E. Pratt, Baltimore, MD 21202, U.S.A. 6: Faculty of Agriculture, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada

Publication date: January 1, 2010


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