Dietary lipid requirement of grouper, Epinephelus malabaricus, and effects on immune responses

摘要

A growth trial was conducted to determine the dietary lipid requirement and its effects on immune responses of juvenile grouper. Purified diets with five dietary lipid levels (0%, 4%, 8%, 12% and 16%; fish oil/corn oil = 1: 1) were each fed to triplicate groups of grouper (mean initial weight: 4.43 +/- 0.07 g) in a recirculating rearing system maintained at 29 +/- 1 degreesC for 8 weeks. Weight gain was highest (P < 0.05) in fish fed diets with 4-12% lipid, followed by the 16% lipid group, and lowest in fish fed the lipid-free control diet. Feed efficiency (FE) and protein efficiency ratio (PER) in fish followed the same pattern of weight gain. Body lipid content was highest in fish fed with 12% and 16% lipid diets, followed by 4% and 8% lipid groups, and lowest in fish fed the control diet. Fish fed with the control diet had lower survival than the other dietary groups. Fish fed with lipid-containing diets had higher white blood cell (WBC) count and respiratory burst activity of leukocyte than fish fed with the control diet. Plasma lysozyme activity of fish fed with 12% and 16% lipid diets were higher than for fish fed with less than or equal to 4% lipid diets. Alternative complement activity (ACH50) was higher in fish-fed diets with greater than or equal to 8% lipid than fish fed with the control diet. Analysis by second-order regression of weight gain indicated that the optimal dietary lipid level in juvenile grouper is about 9%. Four percent of dietary lipid appears to meet the minimal requirement for grouper. These data also suggest that dietary lipid supplementation enhances the immune response of grouper.