Effects of dietary supplementation of Gracilaria extraction fractions on growth performance, fillet quality, oxidative stress and immune responses in European seabass (Dicentrarchus labrax)

By-products generated from the seaweed (SW) industry´s extraction processes have potential applications as feed supplements for aquafeeds. SW extracts contain natural pigments and compounds with antioxidant and immune-stimulant properties [1, 2]. In spite of their beneficial effects, SW extracts may contain compounds with anti-nutritional effects when supplemented in diets, negatively affecting fish growth performance, welfare and ultimately fillet quality. This study appraised the effects of two methanolic fractions extracted from the red SW (Gracilaria sp.), supplemented in European seabass (Dicentrarchus labrax) diets. Three experimental diets were prepared: (i) a control diet without supplementation (CTRL), (ii) a control diet supplemented with the Gracilaria methanolic extract (GE, 0.5%), or (iii) a control diet supplemented with the insoluble residue of the extraction (GR, 4.5%). After 42 days of feeding, the growth performance, digestive enzymes activities, fillet pH and colour, skin colour, and immune and oxidative stress responses were analysed.