Effects of Isatis root polysaccharide on non‐specific immune responses and nutritive indices in obscure pufferfish,Takifugu obscurus

This study examined the effects of Isatis root polysaccharide (IRPS) on the growth and non‐specific immunological responses of obscure pufferfish (Takifugu obscurus) as well as the potential of using this Traditional Chinese Medicine for disease prevention. The antioxidant capacities, lysozyme and complement C3 activities in phagocytosis, erythrocyte C3b receptor rosette rates, respiratory burst activity, body weight increase (BWI), feed conversion ratio (FCR) and several other nutritive indices were determined in pufferfish fed a control diet or diets containing either a low or high level of IRPS. The results showed that IRPS played a positive role in regulating the leukocyte phagocytic rate, respiratory burst and antioxidant enzymes. The IRPS‐fed fish showed an increased BWI and reduced FCR compared with pufferfish fed the control diet. The significant alterations of non‐specific immune response parameters in fish fed the less IPRS diet were rapid, occurring within 7 days, but were then reduced, whereas those in fish fed the more IRPS diet peaked at 10–15 days of treatment but were maintained for at least 30 days. Isatis root polysaccharide activates host immune function, improves phagocytosis by macrophages and exerts direct antimicrobial and antiviral effects, thereby helping to resist infection.