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

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. (C) 2003 Elsevier Science B.V. All rights reserved.