Stress induced elevation of plasma cortisol in adult female coho salmon (Oncorhynchus kisutch), is reflected in egg cortisol content, but does not appear to affect early development

Abstract

Circulating levels of cortisol, the major corticosteroid among teleosts, increase in response to environmental Stressors. Cortisol has also been reported to be present in the freshly ovulated eggs of a number of teleost species. Since environmental Stressors have been implicated in the decrease of egg quality in salmonids, this study was conducted to investigate possible connections between egg cortisol content and subsequent viability. A physical Stressor applied to a single group of adult female coho salmon (Oncorhynchus kisutch), during the final two weeks of oogenesis appeared to result in significantly elevated plasma cortisol levels (227.5 ± 61.5 ng/ml) above those observed in a single group of control animals (141.0 ± 42.7 ng/ml), although other factors cannot be ruled out. Mean egg cortisol content (25.3 ± 0.77 ng/g) was significantly higher in the disturbed than in the undisturbed females (9.90 ± 0.94 ng/g), suggesting that cortisol content in eggs of salmonids is reflective of plasma levels during late oogenesis. Gonadosomatic index was unaffected by the treatment, although there was some evidence to suggest that elevated cortisol levels may have hastened ovulation in the experimental group. Paired groups of eggs from single females having either unmanipulated (37.0 ± 5.4 ng/g) or artificially elevated (232.7 ± 13.9 ng/g) levels of cortisol showed no significant differences in terms of time to, or synchrony of hatch, yolk sac to body weight ratio at hatch, growth from hatch to 52 days post fertilization (dpf), or percent mortality. Cortisol was seen to clear rapidly from eggs in both experimental and control groups soon after fertilization, and there was no significant difference observed between groups by 8 dpf, suggesting that maternal cortisol clears from developing embryonic salmon by the late eyed stage and may not be a factor in later development.