The experiment was to investigate the effect of different dietary lipid levels on the growth performance, nucleic acids, leptin and adiponectin as well as their receptor gene expression in juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Six groups of the juveniles with 40 days of age in triplicate were fed for 90 days using 6 iso‐nitrogen (34% dietary protein) diets. The 6 diets were control diet contained 0.35% of lipid, without lipid supplementation, and the other diets were added different doses of fish oil to make the different dietary lipid levels of 3.35%, 6.35%, 9.35%, 12.35% and 15.35% based on per kg of dried feed. The samples of whole fish and major tissues/organs were randomly taken at 0 and 90 days for determination, respectively. The main results were as follows: compared with the control diet, the diets with different lipid supplementation improved significantly (p < .05) the specific growth rate (SGR), crude fat, nucleic acids, adiponectin receptors 1 and 2 (AdipoRs 1 & 2) gene expression and serum leptin level in juvenile GIFT tilapia. However, the diets with different lipid supplementation reduced significantly (p < .05) the feed conversion ratio (FCR), hepatosomatic index (HSI), crude protein, leptin receptor (LepR) gene expression and serum adiponectin level. There was no significant effect (p > .05) on the survival rate (SR) in the juveniles fed the diets with different lipid supplementation. In conclusion, the diets with different lipid supplementation could affect significantly the SGR, FCR, HIS, nucleic acids, crude fat and protein, leptin and adiponectin levels and their receptor gene expression of the juveniles. The optimal dietary lipid level was 10.52% for SGR and 10.61% for FCR based on the second‐order polynomial regression analysis between dietary lipid levels against the SGR and FCR of the juveniles, respectively, in the experiment.

The main purpose of the present study was to evaluate the anti-inflammatory activity of Lactococcus lactis BL52 and isolate active substances responsible for anti-inflammatory activity. Head-kidney (HK) macrophages were used for in vitro bioassay-guided isolation, and the structure of the two peptides was identified by mass spectrometry analysis. Lipopolysaccharide (LPS)-induced inflammatory responses in Ctenopharyngodon idella were also examined to evaluate the in vivo anti-inflammatory activity of active substances. Two active peptides were isolated by HPLC from L. lactis BL52, and an in vitro anti-inflammatory assay demonstrated that peptide ALBL1 and ALBL2 dose-dependently inhibited LPS-induced inflammatory cytokines TNF-α, IL-6, and IL-1β and inflammatory factors NO and PGE 2 production in macrophages (p < 0.05). After being treated with 20 mg/Kg peptide ALBL1 and ALBL2, the expression levels of TNF-α, IL-6, IL-1β, NO, and PGE 2 were significantly inhibited (p < 0.05). Results from the in vivo test showed that when the concentration of peptide ALBL1 and ALBL2 reached 30 mg/Kg, the LPS-induced upregulations of TNF-α, IL-6, IL-1β, NO, and PGE 2 were prevented. In addition, peptide ALBL1 and ALBL2 blocked the expression of Toll-like receptor 2 (TLR2) and then suppressed the phosphorylation of nuclear transcription factor-kappa B (NF-κB) p65 and degradation inhibitor of IκBα. Moreover, C. idella treated with peptide ALBL1 and ALBL2 can relieve pathological inflammatory responses caused by LPS. These results suggest that the anti-inflammatory properties of peptide ALBL1 and ALBL2 might be a result from the inhibition of IL-6, IL-1β, and TNF-α expressions through the downregulation of Toll2/NF-κB signaling pathways.