Oils Combination with Microalgal Products as a Strategy for Increasing the N-3 Long-Chain Polyunsaturated Fatty Acid Content in Fish Oil-Free Diets for Meagre (Argyrosomus regius)

Abstract

Diversification of species and ingredients is essential for further developing aquaculture production. The present study aimed to evaluate the potential of a blend of microalgae oils and poultry oil as total replacers of fish oil in aquafeeds, a fast-growing species for aquaculture diversification, that was shown to require high dietary n-3 LC-PUFA levels. For that purpose, meagre juveniles ( $2.74\pm 0.01$  g initial body weight) were fed one of the four experimental diets for 30 days. A control diet (FO diet) was based on 5% fish oil and 7% of rapeseed oil, whereas in the other three diets, fish oil was totally replaced by either poultry oil only (PO diet), or blending poultry oil and one of two commercial algal oils (ED and DD diets). Growth performance, tissue composition, and the expression of genes related to fatty acid biosynthesis, antioxidant defense system, and heat shock proteins were determined. Diets with blends of poultry and microalgae oils supported good growth and feed utilization of meagre. Besides, these diets maintained high DHA tissue contents and good fillet lipid quality indices, like in those fish fed the control diet containing fish oil. Furthermore, the meagre fed ED diet showed the highest expression of gpx, in agreement with the highest dietary polyunsaturated fatty acid content. These results demonstrated the good potential of blending these two commercial microalgae oils with poultry oil to completely replace fish oil cost-effectevily in diets for meagre. In contrast, PO as the sole replacer of fish oil was not able to support fish growth performance and tissue contents of n-3 LC-PUFA, leading to an increased thrombogenic index in fish fillets. Additionally, the low dietay n-3 LC-PUFA content of PO diet upregulated the relative expression offads2 while downregulating gpx compared to microalgal diets.