Sea urchin (

Sea urchin processing practices by the canning industry result in a large volume of waste due to a high fraction of inedible parts, in special the gut, that can still be a valuable source of bioactive compounds. Therefore, this work aimed to thoroughly characterise gut biomass from Paracentrotus lividus evaluating its bioactive potential. The gut biomass was evaluated in terms of bioactive capacity, and biochemical composition in both males and females. Although no statistical differences were found between sexes in any of these parameters, this study provided a proof of concept on the potential of sea urchin's gut, obtained as a co-product in the sea urchin industry, for feed supplementation. The gut biomass exhibited a high antioxidant capacity (IC50 ≈ 0.5–1.0 mgDW mL−1 in four different assays) and bactericidal activity (IC50 < 1.0 mgDW mL−1 against Vibrio parahaemolyticus, Edwardsiella tarda, and Tenacibaculum maritimum). The gut co-product can also be used as a source of phenolic compounds, carotenoids, and PUFAs, with contents of 4.6 ± 0.4, 2.4 ± 0.8, and 93.0 ± 3.1 mg gDW−1, respectively. Overall, the sea urchin's gut seems a valuable product with a remarkable potential for use in aquafeeds as a source of bioactive compounds