Effects of heat stress on biochemical parameters and heat shock protein family A (Hsp70) member 5 (HSPA5) mRNA expression in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) is a cold-water species of salmonid, and high temperatures are a significant threat to its aquaculture. In order to understand the degree of the heat stress response and the mechanisms involved, full-sibling inbred O. mykiss individuals were sampled at 18, 21, 23, 24, 25 and 26°C to investigate changes in some serum biochemical parameters, as well as in the mRNA expression of heat shock protein family A (Hsp70) member 5 (HSPA5; also known as glucose regulated protein 78 (GRP78)) in different tissues (liver, mid-kidney, heart, spleen and brain). At 21°C, there was a significant increase in the spleen macrophage respiratory burst and a significant decrease in superoxide dismutase activity compared with 18°C (P<0.05). Malondialdehyde peaked at 23°C, whereas alanine transaminase and aspartate aminotransferase activity were both twofold higher at 25 and 26°C compared with that at 18°C. The Ca2+, Mg2+, PO43– and glucose (Glu) content of serum declined significantly at 21°C relative to 18°C (P<0.05). The expression of HSPA5 mRNA responded in a temperature- and tissue-specific manner to heat stress. Except for in the spleen, HSPA5 mRNA expression was significantly higher in all tissues at 25 and 26°C than that at 18°C (P<0.05). These results indicate that heat stress causes oxidative damage, decreases the Ca2+, Mg2+, PO43– and Glu content of serum and induces HSPA5 mRNA expression.