Effects of Cold Stress on Skin Color, Immuno-Antioxidant Function, Muscle Compositions, and Intestinal Microbiota of Red Tilapia During Overwintering

Cold stress due to overwintering is considered a major issue limiting the development of the red tilapia (Oreochromis spp.) industry. This study was the first to systematically investigate the effects of cold stress on skin color, immuno-antioxidant function, muscle compositions, and intestinal microbiota of red tilapia during overwintering. Fish (initial weight: 72.71 ± 1.32 g) were divided into the cold stress group (cold) and the control group. In the control group, the water temperature (WT) was maintained at 20°C, which is consistent to with the overwintering WT indoors or greenhouse in the local area. In the cold group, the WT was decreased from 20°C to 8°C by 2°C per day during the experiment. At the end of the experiment, we found that the L^∗ value of fish ventral skin in the cold group was lower than that in the control group (p < 0.05). The superoxide dismutase (SOD), malondialdehyde (MDA), glutathione (GSH), catalase (CAT), and total antioxidant capacity (T-AOC) activities were higher, but complement 3 (C3) and complement 4 (C4) activities were lower in the liver of cold group fish than those in the control group (p < 0.05). For the gill tissue, the SOD, MDA, and GSH activities were higher, but the C3 activity was lower in the cold group than those in the control group (p < 0.05). The total amino acid (TAA) content in the muscle of fish in the cold group was higher than that in the control group (p < 0.05). 16 s rRNA analysis showed that the intestinal microbial abundance and alpha diversity of fish in the cold group decreased (p < 0.05). Component analysis revealed a significantly higher relative abundance of Cetobacterium spp. in the fish of the cold group. The findings of this study will provide a valuable understanding of fish cold stress during overwintering, which will contribute to facilitating the breeding of new cold-resistant varieties of red tilapia in the future.