Senegalese sole juveniles can cope with diets devoid of supplemental fish oil while preserving flesh nutritional value

A growth trial was conducted to test the growth potential and nutrient utilization of Senegalese sole fed diets with increasing substitution of supplemental fish oil (FO) by vegetable oil (VO) blends. Triplicate groups of twenty Senegalese sole juveniles (12g) were fed to satiation over a period of 12weeks with 6 extruded diets containing 570g protein/kg DM and 90g lipid/kg DM. Two blends of VO were tested (A and B) with two FO substitution rates 50% (VO50A and VO50B) and 100% (VO100A and VO100B). A concomitant replacement of 50% fish meal and 50% FO (VO50PP), and a control diet (CTR) containing only FO, were also evaluated. After 12-weeks feeding the dietary treatments did not affect growth performance and final body composition. Muscle eicosapentaenoic acid (EPA) was reduced in all treatments compared to CTR, but docosahexaenoic acid (DHA) was only reduced in the VO50PP group. FO substitution led to a general increase of muscle linoleic acid (18:2 n−6, LOA) with VO50PP inducing maximal levels (15% vs 6% in FO diet). Lipogenic enzymes (FAS, ME and G6PD) as well as long chain fatty acid elongation (elov5) and desaturation (Δ4 desaturase) were not affected by dietary treatments. Results suggest that Senegalese sole can cope with high levels of VO without compromising growth performance or nutrient utilization. Despite differences in muscle fatty acid profile, fish fillet had good nutritional value. •Vegetable oil blends can substitute up to 100% of fish oil without impairing growth.•Elongase 5 and Δ4 desaturase expression were unaffected by fish oil substitution.•All sole fillets maintained a good nutritional value for human consumption.