| Summary: | 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.
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