TOTAL REPLACEMENT OF FISH OIL BY BLENDED VEGETABLE OIL ON GROWTH PERFORMANCE AND LIPID METABOLISM IN DIFFERENT STRAINS OF GIBEL CARP (CARASSIUS GIBELIO)

To investigate the effects of total replacement of fish oil by blended vegetable oil on the growth and lipid metabolism in different strains of gibel carp (Carassius gibelio), two iso-nitrogen and iso-lipid formulated diets were prepared using the fish oil (FO) and bended vegetable oil (BVO, rapeseed oil﹕ soybean oil﹕ palm oil=55%﹕25%﹕20%, to mimic the fatty acids profiles of fish oil) as the lipid sources. Gibel carp CAS Ⅲ A strain: (5.01±0.05) g and CAS V F strain: (5.02±0.05) g were assigned to two groups, feeding with the FO and BVO diets for 70d. Concerning the effects of lipid source, the feeding rate (FR) was significantly higher while the feed efficiency (FE) was significantly lower in the BVO group, as compared to the FO group (P<0.05). Enhanced expression levels of srebp-1c and acc were found in the muscle, leading to a significant lipid deposition in both strains of gibel carp (P<0.05). The BVO diet changed the fatty acid composition of muscle significantly, up-regulating and down-regulating the relative contents of Σn-6 PUFA and Σn-3 PUFA, respectively (P<0.05). In terms of strain effects, the F strain showed significantly lower FR but significantly higher FE than the A strain, regardless of dietary lipid sources (P<0.05). Compared to the A strain, the expression levels of hsl and aco3 in the muscle, as well as aco3, fabp1b and fatp1 in the liver of the F strain were significantly higher (P<0.05). Furthermore, the F strain had significantly lower levels of lipid content than the A strain (P<0.05), which suggested that the F stain might have better ability to utilize the dietary lipid for energy expenditure. The dietary lipid sources and strains interacted to affect the specific growth rate (SGR) of gibel carp (P<0.05), but the F strain fed the BVO diet showed no variations with the A strains fed the FO diet, implying the great potential of vegetable oils usage in the diets of the F strain. Overall, the present study demonstrated the differences on the utilization of dietary lipid sources and its related molecular mechanisms in different strains of gibel carp, which could provide information for the dietary lipid sources selection and genetic breeding in gibel carp.