EFFECTS OF DIFFERENT DIETARY PROTEIN LEVELS ON SERUM BIOCHEMICAL INDICES AND EXPRESSION OF LIVER HSP70 mRNA IN GIFT TILAPIA (OREOCHROMIS NILOTICUS) UNDER LOW TEMPERATURE STRESS

Three Groups of GIFT tilapias (Oreochromis niloticus) were fed with protein levels at 25%, 38% and 50%, respectively at 27℃ in 56 days. The initial body weights were (27.642.79) g. Uniform sizes of fish were selected for low temperature stress test at the end of rearing management. Tilapias in the experiment group were subjected to 14℃, and some biochemical indices in their serum and the expression of HSP70 mRNA in liver were examined over 0-24h. The results showed that, before low temperature stress, the 50% protein level group had highest serum glucose (GLU), total protein (TP), triglycride and cholesterol level; Serum glutamic-pyruvic transaminase (ALT) and glutamic-oxaloacetic transaminase (AST) activities was also increased. After low temperature stress, in the 50% protein level group, serum glucose (GLU), total protein (TP), triglyceride and cholesterol level decreased within 24h, while glutamic-pyruvic transaminase (ALT) and glutamic-oxaloacetic transaminase (AST) activities increased at first and then gradually declined. In 25% and 38% protein groups, serum glucose (GLU) level and glutamic-pyruvic transaminase (ALT) activity increased within 24h, whereas serum ALT, alkaline phosphatase (AKP), TP and cholesterol level increased at first and then decreased. Serum lysozyme activity and expression level of HSP70 mRNA in liver of all groups also increased at first and then gradually declined. In conclusion, diet supplemented with high protein level could improve serum protein, blood sugar and lipid level and enhance resistance to low temperature, but could cause liver damage due to decomposition pressure; and could increase feed cost. Therefore, in production, the proportion of protein in the feed should be arranged according to the practical need of tilapia.