Effects of Thermal Stressors on Growth-Related Gene Expressions in Cultured Fish

Growth in fish is regulated by the growth hormone (GH)-growth hormone receptor (GHR)-insulin-like growth factor-1 (IGF-1) axis. However, the effect of severe acute stressors on the GH-IGF-1 axis in fish is not well understood. The present study determined the changes in mRNA expression of growth-related genes gh, ghr, and igf and the redox state in coho salmon (Oncorhynchus kisutch), in response to severe acute stress. Severe stress consisted of exposure to heat shock (adequate rearing temperature +11 °C for 2 h). The plasma expression patterns of redox state-related biomarkers, such as glutathione, lipid peroxides, and superoxide dismutase, in response to heat shock suggest that heat shock might induce oxidative stress in fish. After exposure to heat shock, ghr mRNA levels in the pituitary glands and liver increased, whereas levels decreased 48 h post-stress. Hepatic igf1 mRNA expression levels gradually decreased in response to the stressor. On the other hand, the pituitary gh mRNA expression did not change in response to the stressor. These findings showed that a heat shock-induced oxidative stress could affect the redox state and the expression of several growth-related genes in coho salmon. The results of this study also suggest that the expression of several growth-related genes in fish may be affected differently by the types and strength of stress.