Effect of feed supplementation with seaweed wracks on performance, muscle lipid composition, antioxidant status, digestive enzyme activities, and plasma biochemistry of gilthead seabream (Sparus aurata) juveniles

Macroalgal wracks are frequently considered as waste products. However, macroalgae are a rich source of protein and bioactive compounds with antioxidant and antimicrobial activities whose inclusion in aquafeeds is receiving growing attention. The aim of this study was to assess the use of beach-cast macroalgae as dietary supplement for gilthead seabream (Sparus aurata) juveniles. Fish were fed for 93 days with an extruded commercial diet (CD); a CD supplemented with 7% of a dried-powder from a multispecific macroalgal wrack (30.9% Lobophora sp., 21.9% Dictyota sp., 19.6% Asparagopsis taxiformis, 17.5% Cymopolia sp., 1.8% Hypnea sp., 0.2% Laurencia sp., 0.1% Stypocaulon sp., and 8% not determined) (CD+MU7); a CD supplemented with a monospecific macroalgal wrack of 85% Lobophora sp. (CD+MOL7); and a CD supplemented with a monospecific macroalgal wrack of 85% Dictyota sp. (CD+MOD7). Macroalgae were extracted with n- hexanes, ethyl acetate and ethanol, and the antioxidant capacity of extracts was assessed, with ethyl acetate leading to the most active extracts (p < 0.05). The dietary inclusions of a 7% macroalgal wrack did not negatively affect S. aurata survival, growth, body indexes, proximate composition, oxidative status and plasma parameters. Contrarily, fish fed on CD+MU7 and CD+MOD7 showed the highest monoacylglycerols content, while both monospecific diets led to the highest total saturated fatty acids content in muscle (p < 0.05). The digestive enzymes profile was slightly modified (p < 0.05), but without compromising fish performance. Finally, muscle from fish fed on CD+MOL7 seemed to display a better capacity to modulate the glutathione metabolism (p < 0.05). In conclusion, a 7% of macroalgal wracks can be used as a dietary supplement for S. aurata juveniles, depicting an attractive alternative for the effective harnessing of this usually discarded biomass. Macroalgal inclusion may also reduce the use of fish-based ingredients for aquafeeds, diminishing the pressure on pelagic fisheries, and contributing to the blue bioeconomy strategy.