Dietary supplementation with Ganoderma lucidum polysaccharides improves growth performance, intestinal enzyme activity, serum antioxidant capacity and disease resistance of Chinese soft-shelled turtle (Pelodiscus sinensis) against Aeromonas hydrophila infection

Aquaculture species are often exposed to disease challenges and environmental stress, necessitating the use of natural dietary supplements to enhance health and productivity. This study evaluated the effect of Ganoderma lucidum polysaccharide (GLP) on the growth performance, intestinal enzyme activity, serum antioxidant capacity, and disease resistance of the Chinese soft-shelled turtle (Pelodiscus sinensis) against Aeromonas hydrophila infection. A commercial diet (50% crude protein) was supplemented with GLP (50% purity) at 0 (GLP0), 2.5 (GLP25), 5 (GLP50), 7.5 (GLP75) and 10 (GLP100) g/kg feed. A total of 450 soft-shelled turtles (4.00 ± 0.20 g) were randomly stocked into five concrete tanks (1.2 × 0.4 × 0.3 m) in triplicates and fed thrice daily (8:00, 13:00 and 18:00) at a feeding rate of 3–5% body weight for eight weeks, which was adjusted weekly. At the end of the feeding trial, the soft-shelled turtles were challenged with A. hydrophila (2.0 × 107 CFU/ml) by intraperitoneal injection. The results showed that the soft shelled turtles fed GLP50, GLP75 and GLP100 diets had significantly improved weight gain, specific growth rate, feed conversion ratio and survival (%) compared to those fed the control diet (p < .05). All GLP diets significantly enhanced intestinal trypsin and lipase activities, while the GLP50, GLP75 and GLP100 diets also improved intestinal α-amylase activity compared to the control (p < .05). The turtles fed GLP50 and GLP75 diets displayed significantly enhanced serum total superoxide dismutase activity compared to the control (p < .05). GLP supplementation significantly increased serum catalase and glutathione peroxidase activities while reducing serum malondialdehyde content (p < .05). The cumulative mortality decreased significantly at all levels of GLP supplementation after A. hydrophila challenge (p < .05). Polynomial (quadratic) regression analysis indicated optimum GLP levels of 8.33 g/kg for final body weight, 7.56 g/kg for trypsin activity, and 13.52 g/kg for glutathione peroxidase activity. In conclusion, dietary GLP supplementation enhanced growth, digestive enzyme activities, antioxidant capacity, and disease resistance in Chinese soft-shelled turtles, demonstrating its potential as a functional feed additive in aquaculture.