Compared to fish oil alone, a corn and fish oil mixture decreases the lipid requirement of a freshwater fish species, Carassius auratus gibelio

Numerous studies have investigated the use of plant oil to replace fish oil in the formulation of aqua-feeds; however, it is unknown, in general, whether the previously obtained lipid requirement concentrations based on fish oil require adjustments in view of the replacement of fish oil by plant oil. The present study tested the hypothesis that the appropriate dietary lipid concentration for gibel carp, Carassius auratus gibelio may change after fish oil is partially replaced by corn oil in the diet. Seven isonitrogenous diets were formulated using a mixture of fish oil and corn oil as the lipid source, with lipid concentrations ranging from 10 to 213 g kg− 1. A 70-day growing trial was conducted to evaluate the effects of dietary lipid concentrations on the growth performance, fatty acid changes of the muscle/liver, and mRNA relative expression levels of genes involved in lipogenesis. The results showed that the specific growth rate (SGR) increased markedly with dietary lipid concentrations from 10 to 81 g kg− 1, then decreased and got a no statistical change in the 119 to 213 g kg− 1 groups. In the liver and muscle, 16:0 and 18:0 relative contents exhibited a quadratic regression trend associated with dietary lipid concentrations. MUFA content displayed a logarithmic decrease with increasing dietary lipid concentrations, but a logarithmic increase was observed for LC-PUFA content, with 18:2n− 6 and 18:3n− 3 contents increasing linearly with dietary lipid concentrations. In the liver, the relative mRNA expression levels of ACC1 and FAS decreased with increasing dietary lipid concentrations. In conclusion, based on a broken-line analysis of the SGR, the recommended dietary lipid concentration for juvenile gibel carp fed with an equal mixture of corn oil and fish oil was found to be 73.2 g kg− 1, which represented a 47.9% decrease compared to the value obtained using fish oil as the lipid source. Our results indicate that dietary lipid requirement for freshwater fish species might change markedly when fish oil is replaced by plant oil in the diets.