Effects of chronic hypoxia on growth performance, antioxidant capacity and protein turnover of largemouth bass (Micropterus salmoides)

Fluctuations of dissolved oxygen (DO) frequently lead to a hypoxic condition in aquaculture, and hypoxia exerts tremendously adverse effects on fish. The present study mainly investigated the effects of chronic hypoxia on growth performance, antioxidant capacity and protein turnover of largemouth bass (Micropterus salmoides). The fish were exposed to normoxic (86%–95% DO saturation), mild hypoxic (51%–60% DO saturation) and severe hypoxic (17%–26% DO saturation) conditions for 6 weeks, respectively. Results showed that chronic hypoxia significantly reduced the weight gain rate, specific growth rate and feed intake of largemouth bass. The activities of SOD and CAT in serum, as well as SOD and GPX in muscle, were significantly increased in the severely hypoxic condition. The histological analysis showed that the mean diameter of myofiber was significantly decreased during severe hypoxia. Additionally, the levels of gene and protein revealed that chronic severe hypoxia inhibited protein synthesis by downregulating the HIF-1α/REDD1/mTOR signal pathway and promoted protein degradation by activating the pathways of ubiquitin-proteasome, autophagy-lysosome and calcium proteasome. Overall, this study indicated that chronic hypoxia decreased the growth performance of largemouth bass. Meanwhile, chronic severe hypoxia not only enhanced antioxidant capacity, but also contributed to orient in the balance of protein turnover towards catabolism thus causing muscle atrophy. We suggested that for better growth of fish, the dissolved oxygen concentration should be maintained above 60% DO saturation in aquaculture.