Effects of replacing fish oil with wheat germ oil on growth, fat deposition, serum biochemical indices and lipid metabolic enzyme of juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂)

Abstract

Fish oil was one of most important feed ingredients for carnivorous marine fish species, but the production might not cover all the necessary quantity for aquaculture. Meanwhile wheat germ oil could be a potential alternative for fish oil in aquatic feed. Hence, a 70 day feeding trial was conducted to investigate the effects of dietary fish oil replaced by wheat germ oil (WGO) on the growth, lipid and fatty acids deposition, and lipid metabolic enzymes activities of juvenile hybrid grouper (initial weight 55.31 ± 0.68 g), E. fuscoguttatus♀ × E. lanceolatus♂. Six isonitrogenous and isoenergetic experimental diets were formulated with 0%, 20%, 40%, 60%, 80% and 100% replacement of fish oil by WGO. Survival rate, weight gain rate, specific growth rate, and feed conversion ratio were similar among fish fed with different diets. Viserosomatic index and mesenteric fat ratio were significantly increased by dietary WGO. No significant differences were observed in the compositions of whole body, muscle and liver. C18: 3n-3 and C18:2n-6 contents in tissues were significantly increased, but EPA and DHA were significantly decreased by dietary WGO. No significant differences were found on the activities of hepatopancreas lipoprotein lipase, hepatic lipase and fatty acid synthase, while the activity of intestinal lipase was decreased. Total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol in plasma were not affected, but triglyceride was increased by dietary WGO. It can be concluded from the results that about 71.8% dietary fish oil can be replaced by WGO in diets with 50% crude protein and 12% crude lipid for subadult hybrid grouper, and fatty acids deposition and biosynthesis of this species was quite different from that of other fish species.