Responses in growth performance, enzymatic activity, immune function and liver health after dietary supplementation of Porphyridium sp. in juvenile golden pompano (Trachinotus ovatus)

The marine unicellular microalga Porphyridium sp. synthesizes several bioproducts consisting of sulphated polysaccharides, arachidonic acid and phycoerythrin, of which sulphated polysaccharides prominently exhibit antiviral, anticancer, anti‐inflammatory, antioxidative and immunomodulatory properties. This study aimed at appraising the feasibility of Porphyridium sp. in diets for Trachinotus ovatus. Three experimental diets were formulated to contain 0 (PS0), 10 (PS1) and 50 g/kg (PS5) Porphyridium sp. powders. After 6 weeks of feeding trials, the supplementation of Porphyridium sp. significantly boosted the growth performance and activities of digestive enzymes (pepsin and lipase). Fish fed with PS1 and PS5 diets showed greater villus length than those fed with PS0 diet. The antioxidant capacity of fish fed the diet with Porphyridium sp. powders was pronouncedly enhanced via stimulating the Nrf2‐ARE pathway and elevating antioxidant enzyme activities. Moreover, Porphyridium sp. supplementation not only promoted liver health of fish by suppressing mRNA levels of pro‐inflammatory cytokines and apoptotic genes, but significantly boosted non‐specific immunity via up‐regulating the mRNA levels of c‐type lysozyme and complement C4 and down‐regulating the mRNA levels of heat shock protein 70. These results suggest that microalga Porphyridium sp. promotes the growth performance and immune function, and thereby strengthens the health of T. ovatus.