Growth and physiological responses of GIFT Oreochromis niloticus in an in-pond raceway system

In this study, the growth and physiological parameters were compared between tilapia (GIFT Oreochromis niloticus) cultured in a traditional pond and that in an in-pond raceway system (IPRS) for 120 days. For the traditional way, 5 ind./m² (stocking density 1, SD1) were reared, while 180 ind./m² (SD2) and 270 ind./m² (SD3) were cultured in an IPRS. The main objective of this study was to find the appropriate density of tilapia to be cultured in an IPRS. The results showed that after 120 days of culture, the body weight, specific growth rate and absolute growth rate of the SD2 fish were significantly higher than those of the SD1 and SD3 fish. The survival rate, coefficient of variation of weight and feed coefficient rate of SD2 and SD3 tilapia were lower than those of the SD1 tilapia. Compared with SD1 fish at 30 days, the relative expressions of serum cortisol, serum alanine aminotransferase, lysozymal aspartate aminotransferase and hepatic hsp70 mRNA were significantly increased in the SD2 fish.The levels of serum cortisol and glucose in the SD3 fish were significantly higher after 120 days of culture than those in the SD1 fish. Compared with SD1, the levels of SAA, LAA and hepatic hsp70 mRNA expressions of the SD2 fish were significantly higher after 60 and 90 days, while the level of triglyceride was significantly lower during the whole experimental period. The results implied that tilapia in the SD2 were stressed in the early stage of cultivation but gradually acclimated to the environment, while tilapia in the SD3 were stressed for a relatively longer time. Taken together, this study demonstrated that the appropriate stocking density of tilapia cultured in the IPRS might be 180 ind./m² or less in order to obtain a better growth performance than in the traditional culturing mode.