Supplementation of macroalgae together with non-starch polysaccharide-degrading enzymes in diets enhanced growth performance, innate immune indexes, and disease resistance against Vibrio parahaemolyticus in rabbitfish Siganus canaliculatus

Macroalgae with high nutritional value are a potential ingredient for aquafeed. However, the presence of anti-nutritional factors such as non-starch polysaccharides (NSPs) in macroalgae prevents their application. The present study was conducted to investigate whether the supplementation of exogenous NSP-degrading enzymes in macroalgae-containing diets can avoid the above disadvantage in the rabbitfish Siganus canaliculatus. Seven isoproteic (32%) and isolipidic (8%) diets (D1-D7) were prepared for the culture of rabbitfish juveniles lasting 10weeks. D1 without macroalgae and NSP-degrading enzymes were used as control diet, D2-D4 contained 12% dry powder of macroalgae Ulva prolifera, Gracilaria lemaneiformis, or Ulva pertusa, respectively, while D5-D7 were supplemented with 0.05% NSP-degrading enzymes on the base of D2-D4. The results showed that the growth performance of fish-fed D5-D7 displayed as good as those fed D1 and was significantly higher than those fed D2-D4 (P<0.05). The activities of serum lysozyme, superoxide dismutase, and acid phosphatase were significantly elevated in fish-fed diets with addition of macroalgae (D2-D7) compared with fish-fed D1 (P<0.05). The amino acid and fatty acid composition of fillet showed no difference among different dietary groups (P>0.05). By the end of the growth trial, 60 fish from each dietary group were subjected with Vibrio parahaemolyticus challenge by intra-peritoneally injection at 10(5)cfumL(-1) and 0.01mLg(-1) body mass. The survival at day 15 post-challenge in fish-fed D4-D7 was significantly higher than those fed D1. The results demonstrated that macroalgae can be used as a dietary ingredient for S. canaliculatus at 12% when supplemented with 0.05% NSP-degrading enzymes. Moreover, the addition of macroalgae in diet can improve the innate immune capability of S. canaliculatus and enhance the disease resistance against V. parahaemolyticus.