Effects of chronic hypoxia on growth performance and nutrient metabolism in the tiger puffer, <scp><i>Takifugu rubripes</i></scp>

Chronic hypoxia is a common and harmful stress in aquaculture. However, the effects of chronic hypoxia on nutrients metabolism, muscle quality and three hifα isoforms expressions in marine fish species are unknown. In the present experiment, the tiger puffer was divided into the normoxia group (NO, dissolved oxygen [DO] = 6.5 ± 0.5 mg/L) and the chronic hypoxia group (CH, DO = 3.5 ± 0.5 mg/L) for 8 weeks. The growth performance, nutrient metabolism, muscle texture, amino acid and fatty acid compositions were measured. The results showed that chronic hypoxia reduced the weight gain, viscerosomatic index, fish crude lipid content, muscle adhesiveness and chewiness, but increased the feed conversion ratio, fish crude protein content and liver n-3 polyunsaturated fatty acid level. Chronic hypoxia increased glucose and triglyceride contents in the serum, but reduced serum total protein level. Meanwhile, chronic hypoxia inhibits anaerobic glycolysis and lactate content by reducing hif1α, hif3α and glycolysis (hk1 and pfk) related gene expressions in the liver and muscle. Chronic hypoxia reduces liver total protein level by increasing protein synthesis (mtor and glud1) and catabolism (gcn2 and uba1) related genes expression simultaneously. Chronic hypoxia suppresses muscle metabolism by reducing the expression of glucose, lipid, protein and insulin pathway related genes. Our results clarified the effects of chronic hypoxia on growth and nutrients metabolism in tiger puffer, which improved our understanding of hypoxia adaptive mechanism in fish.