Effects of different carbohydrate levels on gill tissue structure, antioxidant capacity and immunity of Micropterus salmoides

In order to explore the effects of different carbohydrates levels on gill tissue structure, antioxidant capacity and immunity of the gill tissue of Micropterus salmoides, three kinds of isonitrogen and lipid feeds with different carbohydrate levels were designed: 7% (L group), 12% (M group), 17% (H group). 360 fish were selected and fed for 8 weeks with an initial weight of (4.0±0.2) g. Through the study of tissue sections, anti-oxidation enzyme and immunoenzyme activity determination, and related mRNA expression, the effect of dietary carbohydrate on gills were analyzed, the results showed that diet in 17% carbohydrate feed can cause the proliferation and fusion of the base cells of the gill lamella, and the shedding of epithelial cells; the content of malondialdehyde (MDA) in the 17% carbohydrate feed and 12% carbohydrate feed was significantly higher than that of 7% carbohydrate feed; the superoxide dismutase (SOD) and peroxidase (CAT) of gill tissue in 17% carbohydrate feed and 12% carbohydrate feed were significantly lower than 7% carbohydrate feed; Antioxidant enzymes (CAT, GPX, SOD1, SOD2, SOD3a and SOD3b) mRNA levels in 17% carbohydrate feed and 12% carbohydrate feed were also significantly lower than 7% carbohydrate feed; in 17% carbohydrate feed and 12% carbohydrate feed acid phosphatase (AKP), alkaline phosphatase (ACP) and lysozyme (LZM) were also significantly lower than the 7% carbohydrate feed; the mRNA levels of immune-related genes (IL-1β, IL-10, IL-15, TNF-α and TGF-1β) and antimicrobial peptides (hepcidin-1 and hepcidin-2) in the 17% carbohydrate feed and 12% carbohydrate feed were significantly lower than those in 7% carbohydrate feed; the apoptosis-related genes(caspase-3, caspase-8, caspase-9) mRNA level in 17% carbohydrate feed were significantly higher than that of the 7% carbohydrate feed and 12% carbohydrate feed; the occluding and claudin-7 mRNA levels of the 17% carbohydrate feed were significantly lower than those of the 7% carbohydrate feed and 12% carbohydrate feed.The study showed that: under the experimental conditions, 17% carbhydrate feed will damage the gill tissue structure , reduce the antioxidant capacity and immune capacity of Micropterus salmoides.