Dietary sulfate-based alginate polysaccharide supplementation boosts growth, gut health, immune response and disease resistance in juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus) fed cottonseed protein concentrate-based diets
Chao Li, Guofeng Chen, Menglin Wei, Hongyu Liu, Beiping Tan, Xiaohui Dong, Qihui Yang, Shuyan Chi, Shuang Zhang, Min Yao
Abstract
To study the dietary prebiotic role of Sulfate-Based alginate polysaccharide (SAP) in cottonseed protein concentrate-based diets, six iso-nitrogenous and iso-lipid feeds were prepared to feed grouper, including a fishmeal control group (FM) was set at 50% fishmeal level, on this basis 5 groups replacing 50% fishmeal protein with cottonseed protein concentrate and supplementing sulfate-based alginate polysaccharide 0%, 1%, 2%, 3% and 4% (SAP0, SAP1, SAP2, SAP3 and SAP4 groups). The healthy and vigorous grouper (initial weight = 8.63 ± 0.01 g) were selected and randomly divided into 6 treatment groups in triplicates (30 fish in each repetition). The feeding experiment was conducted for 8 weeks, followed by a one-week Vibrio harveyi challenge. The experimental results showed that the weight gain and specific growth rate reached the significant maximums in SAP2 and SAP3 groups (P < 0.05). The malondialdehyde and triglyceride levels in serum decreased, while the antioxidant indicators and non-specific immune enzymes activity (lysozyme, acid phosphatase, alkaline phosphatase) in serum and intestinal tissue got increased (P < 0.05). The intestinal digestive enzymes activity and histomorphology indices (plica height, plica width and muscle layer thickness) were increased (P < 0.05). Microbial sequencing revealed that the ACE and Chao1 indices increase firstly and then decreased, while the Shannon and Simpson indices showed a decreasing trend (P < 0.05). The expression level of pro-inflammatory factors (IL-1β and TNF-α) was down-regulated, yet the expression of anti-inflammatory factors (IL-10) was up-regulated in intestinal tissue (P < 0.05). The cumulative mortality of Vibrio harveyi challenge was significantly reduced (P < 0.05). In one word, the adverse effects on growth, immunity and intestinal health of grouper feeding cottonseed protein concentrate-based diets were repaired by the supplementing sulfate-based alginate polysaccharide. According to the binary regression analysis of specific growth rate among SAPs treatments, the optimum level of supplementing sulfate-based alginate polysaccharide of grouper was 2.25%.