Improving low-temperature stress tolerance of tilapia, Oreochromis niloticus: A functional analysis of Astragalus membranaceus

A 54-day experiment was conducted to investigate the effects of dietary supplementation of Astragalus membranaceus extract powder (AMEP) on the low temperature tolerance of genetically improved farmed tilapia, Oreochromis niloticus. The base diet was supplemented with 0.0% (NC), 0.1% (NP0.1), 0.2% (NP0.2), and 0.4% (NP0.4) AMEP. Tilapia with an initial body weight of 21.35 +/- 0.17 g were fed three times a day for 14 days at 30 degrees C and then fed for 40 days while the water temperature decreased at a rate of 0.5 degrees C/day. The results showed that survival, final weight, and the rate of weight gain in fish in the NP0.1, NP0.2, and NP0.4 groups were higher than those of fish in the NC group. The contents of glucose, triglyceride, cholesterol, and nitric oxide in the serum of fish fed diets supplemented with AMEP were all significantly lower than those of fish in the NC group. In contrast, fish fed with AMEP-supplemented diets had higher liver superoxide dismutase, glutathione peroxidase and catalase activities, and lower malonaldehyde content than those of fish in the NC group at 10 degrees C. The expression of the growth-arrest-specific 2 gene in the liver was significantly lower in the NP0.2 and NP0.4 groups than in the NC group. The results of this study demonstrated that the optimal level of AMEP supplementation was 0.2% under the conditions used in the current study. Optimum dietary AMEP can promote growth performance and facilitate the survival of tilapia under low-temperature stress.