Long-term feeding of vegetable oils to Senegalese sole until market size: Effects on growth and flesh quality. Recovery of fatty acid profiles by a fish oil finishing diet

• Total fish oil substitution does not impair growth or feed utilization.
• Sole selectively retains highly unsaturated fatty acids (ARA and DHA).
• Sole fillets fed high VO levels are well accepted by consumers.
• Sole fillets fed high VO levels provide 1.5 times the RDI level of EPA + DHA.

The present study evaluates the long term (5 months) effects of feeding vegetable oil-based diets to Senegalese sole (Solea senegalensis) until market size. Extruded isonitrogenous and isoenergetic diets (56% crude protein and 20 kJ/g) were formulated to substitute 0 (CTRL), 50 (VO50) and 100% (VO100) of FO by a VO blend (rapeseed oil, RO, soybean oil, SO, and linseed oil, LO). A concomitant replacement of 50% FM and FO (VO50PP50) by plant protein sources (pea, soybean meal, potato concentrate, corn and wheat gluten) and oils was also evaluated. After the growth trial (140 days), fish were fed a fish oil-based diet (CTRL) over a period of 26 days and growth, flesh quality and organoleptic properties were determined.Results show that it seems possible to substitute up to 100% of FO by a VO blend, as well as concomitantly substituting 50% FO and FM by vegetable sources in on-growing Senegalese sole diets, without compromising growth performance and feed utilization. This species selectively retains highly unsaturated fatty acids (ARA and DHA) and seems to adapt well to a low dietary supply of these FAs. At the end of the growth out experiment fish fed VO50 diet showed a similar n − 3 HUFA profile to the CTRL fed fish. Total FO substitution resulted in a strong reduction of muscle EPA content that was totally recovered after 26 days of re-feeding with a FO based diet. Despite the observed changes in fatty acid composition, sole fillets from fish fed 100% VO are very well accepted by fish consumers and still are good nutritional value end-products for human consumption, providing 1.5 times the RDI level (0.4 g per 100 g of muscle) of EPA + DHA.