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Measurement of plasma cortisol and histometry of the interrenal gland of juvenile pre-smolt coho salmon (Oncorhynchus kisutch Walbaum) during cold temperature acclimation. Allan , Gerald D.


Juvenile, pre-smolt coho salmon were subjected to a decrease in environmental temperature from 12°C (temperature of acclimation) to 2°C over a period of approximately 72 hours. During this time, plasma Cortisol values were estimated by the competitive protein binding (CPB) technique. In addition, an histometric analysis of the interrenal tissues of these fishes was performed as a measure of interregnal activity. Experimental results indicated that fluctuations in plasma Cortisol concentrations occurred within 120 hours of the initiation of temperature alteration. Control levels for plasma Cortisol were 2.9 ± 0.75 ug cortiso1/100 ml plasma (mean ±S.D.). Maximum plasma Cortisol concentration, observed at hour 84 after temperature alteration, was 27.0 ± 2.8 ug cortisol/100 ml plasma (mean ± S.E.). By hour 96 experimental cortisol values returned to a level just slightly above those of controls and did not change significantly after that time. Measurements of interrenal nuclear diameters showed a significant increase in interrenal activity 14 days after initiation of exposure to cold. This level of interrenal activity was maintained until the experiment was terminated (20 days exposure to cold). It is concluded from this study that during acclimation to cold temperature, plasma cortisol values of juvenile, pre-smolt coho salmon demonstrate an early and rapid increase (within 120 hours exposure to colder temperature) followed by an equally rapid decrease to a level just slightly above that of controls. Furthermore, it is concluded that juvenile, pre-smolt coho salmon treated in this manner show no histologically demonstrable increase in interrenal activity until well after plasma cortisol values have become stabilized at a level slightly above that of controls (14 days exposure to cold).

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