Influence of dietary lipid levels on growth, nutrient utilization, tissue fatty acid composition and desaturase gene expression in silver barb (Puntius gonionotous) fingerlings

Silver barb (Puntius gonionotus) is considered as a promising medium-sized carp species for freshwater aqua culture in Asia. This study in silver barb was carried out to evaluate the effects of increasing dietary levels of lipid on growth, nutrient utilization, whole-body composition, tissue fatty acid composition and Delta 6 fatty acyl desaturase (Delta 6 fad) gene expression. Fish (11.3 +/- 0.23 g of initial body weight) was fed for 60 days with five experimental diets: FO-0 (control feed); FO-30; FO-60; FO-90 and FO-120 containing 0, 30, 60, 90 and 120 g fish oil kg(-1) diet, respectively. Among the diets, the highest specific growth rate (SGR), protein efficiency ratio (PER) and whole-body lipid content, and the lowest feed conversion ratio (FCR) were recorded with FO-120 diet. The saturated fatty acids (SFA) level in the muscle was significantly (P < .05) increased with the enhanced FO supplementation, whereas monounsaturated fatty acids (MUFA) level decreased. Increased level of fish oil in the diet also enhanced the n-3 PUFA and n-3 LC-PUFA (long-chain polyunsaturated fatty acid) in the muscle and liver. The expression of Delta 6 fad gene was downregulated, whereas the serum biochemical constituents were either remain unchanged or enhanced with increased FO supplementation in the diets of silver barb.