Physiological responses and HSP70 mRNA expression in GIFT tilapia juveniles, Oreochromis niloticus under short-term crowding

Physiological responses and HSP70 mRNA expression to short-term crowding were tested in juveniles genetically improved farmed tilapia (Oreochromis niloticus) (70.43 +/- 4.43g). Fish were kept at control group (5gL(-1)) and stress groups (low density 10gL(-1), medium density 40gL(-1) and high density 70 and 100 gL(-1)) for 48h. Each density was tested in triplicates. The effects of a short-term exposure on the physiological responses of fish were determined before stress (0h) and at 6, 12, 24 or 48h post-crowding. There was a significant increase in serum cortisol, total protein, lysozyme and aspartate aminotransferase (AST) activities in all stressed groups at 24h post-crowding (P<0.05). Serum glucose and alanine aminotransferase (ALT) of 100gL(-1) stressed group were lower than that of the control after 48h of crowding stress (P<0.05). The levels of serum triglyceride and cholesterol in crowding stress with high density were significantly decreased compared with the control group at 48h. The mRNA expression data showed that hepatic HSP70 mRNA levels were markedly elevated at all stressed groups. HSP70 mRNA levels of 70 and 100gL(-1) stressed groups decreased at 48h compared with the 24h post-crowding. The protective ability of HSP70 was limited.