Aspects of cortisol dynamics during the early ontogeny of three species of Pacific salmon (Oncorhynchus sp.)

Seven female coho salmon (Oncorhynchus kisutch), in the final stages of oogenesis, were exposed to mechanical disturbance (chased for 60 seconds with hand net), twice daily over a two week period. There was no significant difference in mean gonadosomatic index between disturbed (4.63 ± 0.19) and undisturbed (4.76 ± 0.34) females. Mean plasma Cortisol level in the disturbed females (227.52 ± 61.51 ng/ml) was higher, though not significantly, than that seen in undisturbed females (140.99 ± 42.70 ng/ml). Mean oocyte Cortisol content (22.13 ± 1.32 ng/gm) was significantly higher in the disturbed, than in the undisturbed females (9.90 ± 0.94 ng/gm). It is suggested that the C or tisol content of freshly ovulated oocytes in salmonids is reflective of the level of circulating Cortisol in the adult female during late oogenesis. Oocytes from 5 female coho salmon were split into paired groups and one half exposed to water containing exogenous Cortisol. The Cortisol immersed groups had a mean oocyte Cortisol content (232.68 ± 13.93) that was significantly higher than that in the paired untreated groups (37.03 ± 5.43). Mean oocyte Cortisol content was monitored from 0 to 56 days post fertilization (dpf). Oocyte Cortisol content was seen to decline sharply after fertilization, and there was no significant difference between paired immersed and control groups by 16 dpf. The immersed groups demonstrated no significant difference in terms of mean time to hatch, mean synchrony of hatch, percent mortality, mean yolk sac to body weight ratio at hatch, or mean length and dry weight up to 56 response, as embryos treated with exogenous Cortisol alone did not display reduced growth, while those receiving the emersion treatment alone did show some significant reduction in weight.Science, Faculty ofZoology, Department ofGraduat