Effects of hypoxia stress on oxidative stress, apoptosis and microorganisms in the intestine of large yellow croaker (Larimichthys crocea)

In order to understand the physiological response of large yellow croaker under hypoxia stress, large yellow croaker with body weight of (31.67 ± 3.69) g was used as the research object. The 96 h hypoxia (2.0 ± 0.1) mg / L stress group and normoxia (7.8 ± 0.5) mg / L control group were set up. The changes of oxidative stress index, apoptosis rate, apoptosis-related gene expression, tissue morphology and microorganisms of large yellow croaker intestine in hypoxia stress group and normoxia control group were analyzed by biochemical detection, paraffin section, qRT-PCR and 16S rDNA sequencing. The results showed that the oxidative stress indexes such as ROS, SOD, CAT, MDA and GSH in the intestinal tissue of the hypoxic stress group were significantly higher than those in the control group. The expression of bax, caspase-3 and caspase-9 mRNA was significantly higher than that of the control group, and the expression of bcl2 mRNA was significantly lower than that of the control group. After 96 h of hypoxia stress, the apoptosis index of intestinal cells in in the hypoxia stress group was significantly higher than that in the control group, the number of intestinal goblet cells decreased, and the height, width of intestinal villi and muscle thickness were significantly lower than those in the control group. There were significant differences in intestinal microorganisms between the hypoxia stress group and the control group. The dominant bacteria involved in energy metabolism under hypoxia stress were Firmicutes and Bacteroidetes, and the dominant bacteria involved in intestinal inflammation were Proteobacteria. Oxidative stress enzyme activity and apoptosis gene expression were significantly correlated with the abundance changes of conditional pathogenic bacteria such as Mycoplasma, Staphylococcus and Pseudomonas, and beneficial bacteria such as Lactobacillus and Clostridium. The above results showed that hypoxia stress caused oxidative stress and apoptosis in large yellow croaker, and changed the intestinal tissue structure and intestinal microorganisms. Intestinal probiotics help fish to resist oxidative stress and apoptosis under hypoxic stress, while conditional pathogenic bacteria have the opposite effect. This study has accumulated basic biological data for the study of the physiological response mechanism of large yellow croaker to hypoxia stress, and provided new understanding for understanding the mechanism of hypoxia affecting fish intestinal health.