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

Circulating levels of cortisol, the major corticosteroid among teleost s, increase in response to environmental stressors. Cortisol has also been reported to be present in the freshly ovulated eggs of a number o f 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 s ubsequent 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 sing le group of control animals (141.0 +/- 42.7 ng/ml), although other fac tors cannot be ruled out. Mean egg cortisol content (25.3 +/- 0.77 ng/ g) was significantly higher in the disturbed than in the undisturbed f emales (9.90 +/- 0.94 ng/g), suggesting that cortisol content in eggs of salmonids is reflective of plasma levels during late oogenesis. Gon adosomatic index was unaffected by the treatment, although there was s ome evidence to suggest that elevated cortisol levels may have hastene d ovulation in the experimental group. Paired groups of eggs from sing le females having either unmanipulated (37.0 +/- 5.4 ng/g) or artifici ally elevated (232.7 +/- 13.9 ng/g) levels of cortisol showed no signi ficant differences in terms of time to, or synchrony of hatch, yolk sa c to body weight ratio at hatch, growth from hatch to 52 days post fer tilization (dpf), or percent mortality. Cortisol was seen to clear rap idly from eggs in both experimental and control groups soon after fert ilization, and there was no significant difference observed between gr oups by 8 dpf, suggesting that maternal cortisol clears from developin g embryonic salmon by the late eyed stage and may not be a factor in l ater development. (C) 1997 Elsevier Science B.V.