Transgenerational effects of stress in sockeye salmon (Oncorhynchus nerka) on offspring fertilization success and embryonic survival Middleton, Collin T.
Fish cope with stress by mounting a primary endocrine response via the sustained release of glucocorticoid steroid hormones – particularly cortisol. Exposure of fish to chronic stress and the sustained release of cortisol is known to have a wide range of effects on physiological processes, although less is known about its effects on reproduction. I utilized wild sockeye salmon from the Fraser River, British Columbia to examine some of the earliest effects of parental exposure to chronic stress and egg exposure to cortisol on viable offspring production. Fraser River sockeye salmon have declined precipitously in numbers and productivity in recent years. Increasingly stressful spawning migrations and the subsequent detrimental effects increased parental stress has on offspring has been put forth as a hypothesis to help explain these recent declines. I simulated chronic stress by periodically chasing female sockeye salmon for 6 weeks prior to ovulation. Egg survival to hatch remained high in both wild (90%) and control (80%) treatments but was significantly reduced as a result of chronic maternal stress (63%; Kruskal-Wallis test, H = 12.64, P = 0.002). To simulate the effect of circulating levels of maternal cortisol, eggs from wild caught females were fertilized in water dosed with control (0 ng/mL), low (300 ng/mL), and high (1000 ng/mL) levels of cortisol. Egg fertilization success remained high in the control group (90%), but was significantly reduced by exposure to both low and high levels of cortisol (78% and 79% respectively; Kruskal-Wallis test, H = 13.27, P = 0.001). Regardless of stress or cortisol exposure, embryos were highly likely to survive to emergence if they hatched. Results from this study indicate that transgenerational effects of stressful migrations are real and this has ramifications to the productivity of populations and spawner fitness. Transgenerational effects of stress may be one explanatory mechanism contributing to declines in Fraser River sockeye salmon.
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