LAUSR

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 10 weeks. 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 105 cfu mL−1 and 0.01 mL g−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.