Effects of heat stress on serum Cortisol, alkaline phosphatase activity and heat shock protein 40 and 90β mRNA expression in rainbow trout Oncorhynchus mykiss

The enhanced expression of heat shock proteins (Hsps) in organisms is associated with environmental temperatures. For rainbow trout ( Oncorhynchus mykiss ), high temperature is a major abiotic stress limiting its growth and productivity. In the present study, we have investigated serum Cortisol (COR) and alkaline phosphatase (AKP) activity as well as Hsp40 and Hsp90β mRNA expression in different tissues (gill, liver, spleen, heart, brain and head kidney) of rainbow trout under unstressed (18°C) and heat-stressed (25°C) conditions. Consequently, COR at 8 H, and heat stress recovering (HSR) AKP at 2, 8 and 12 H were significantly up-regulated in the heat stressed group (P < 0.05). Hsp40 and Hsp90β mRNA expressions were significantly up-regulated in all tissues and responded to heat stress in a tissue- and time-specific manner. Their expression in heart and brain were relatively high in the unstressed group compared with other tissues (P < 0.05). During heat stress, Hsp40 and Hsp90β in all tissues showed the first rise after falling trend, and the highest induction was recorded in the spleen (P < 0.05). Hsp40 in heart and brain, and Hsp90β in liver and brain did not return to the comparison group (0 h) after HSR. The results indicate that Hsp40 and Hsp90β are more important in dealing with heat-induced stress and mainly afforded protection in liver, heart and brain. In addition, cells may be damaged under heat stress with increasing AKP activity and elevating COR, which regulates energy metabolism and fights environmental pressure to maintain homeostasis of rainbow trout.