Abstract
The study evaluated the change of stress indicators in plasma and mRNA expression levels of stress-related genes in head-kidney and liver of walleye pollock, Gadus chalcogrammus according to acute salinity fluctuation. Walleye pollocks were exposed for 24 hours in five groups, as salinity are 34, 30, 25, 20, and 15 psu. The levels of hematocrit (Ht), glutamic oxaloacetate transaminase (GOT), cortisol, glucose, and superoxide dismutase (SOD) in plasma were increased as the salinity of the breeding water decreased. Ht increased with 37.5 ± 1% at 20 psu. GOT with 41.0 ± 5.03 U/L, cortisol with 882.73 ± 32.73 ng/mL, and glucose with 67.67±11.6 ng/dL increased a significant difference at 25 psu. The SOD activity levels in plasma were highest at 15 psu with 3.51 ± 0.13 U/mL. Plasma hemoglobin (Hb) and glutamic pyruvic transaminase (GPT) did not show a statistically significant difference according to salinity, but showed a tendency to increase as the salinity decreased. Total protein (TP) levels in plasma were the highest with 5.9 ± 0.61 g/dL at 25 psu. The relative mRNA expression of stress-related genes was investigated in the head-kidney and liver of walleye pollocks, and the mRNA expression of steroidogenic acute regulatory protein (StAR) and heat shock protein 70 (HSP70) increased, as the salinity decreased from 25 psu, whereas glucocorticoid receptor (GR) mRNA expression decreased as the salinity decreased. These results suggest that walleye pollocks become stressed-condition to salinity below 25 psu, but homeostasis can be maintained up to 15 psu in short-term.
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