No abstract

The green alga Haematococcus pluvialis JNU35 is enriched in astaxanthin, linoleic acid and linolenic acid. H. pluvialis JNU35 can be used as an immunostimulant in aquatic feed. Here, the role of H. pluvialis JNU35 in mediating growth, antioxidation, immunity and liver function of Trachinotus ovatus was examined through feeding test. HP0, HP1 and HP5 diets containing 0, 10 and 50 g/kg H. pluvialis JNU35 were prepared for 6-week feeding. It is shown that the supplement of H. pluvialis JNU35 in diet significantly triggers fish growth through elevating activities of digestive enzymes, food intaking, villus length and upregulating growth hormone and insulin-like growth factor. H. pluvialis JNU35 supplementation protected from oxidative stress through the Nrf2-ARE pathway and thus elevated activities of antioxidant enzymes. Meanwhile, H. pluvialis JNU35 supplementation protected liver function by declining lipid deposition, inhibiting hepatocyte apoptosis, upregulating anti-inflammatory cytokines and downregulating pro-inflammatory cytokines. Non-specific immune ability of fish was also promoted by regulating expressions of complement 4, c-type lysozyme and heat shock protein 70 in HP1 and HP5 diets. The blood health state of fish was improved by H. pluvialis JNU35 supplementation. In conclusion, H. pluvialis JNU35 promoted growth, antioxidation, immunity and liver function in T. 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.