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 degrees C to investigate changes in some serum biochemical parameters, as well as in themRNAexpression of heat shock protein familyA(Hsp70) member 5 (HSPA5; also known as glucose regulated protein 78 (GRP78)) in different tissues (liver, mid-kidney, heart, spleen and brain). At 21 degrees C, there was a significant increase in the spleen macrophage respiratory burst and a significant decrease in superoxide dismutase activity compared with 18 degrees C (P < 0.05). Malondialdehyde peaked at 23 degrees C, whereas alanine transaminase and aspartate aminotransferase activity were both twofold higher at 25 and 26 degrees C compared with that at 18 degrees C. The Ca2+, Mg2+, PO43- and glucose (Glu) content of serum declined significantly at 218C relative to 18 degrees 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 degrees C than that at 18 degrees 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.