In the present study, the effects of polyphenols extracted from olive mill wastewaters (OMWW) were investigated in the narrow clawed Astacus leptodactylus in a 24 week-feeding trial. 0.5 and 5.0 g of OMWW polyphenolic extract were mixed with 1 kg of basic diet to generate OMWW-LC (Low Concentration) diet and OMWW-HC (High Concentration) diet. Growth performances, antioxidant and immunological parameters, microbiota, and FA composition were evaluated. Growth performances (specific growth rate; feed conversion ratio; protein, lipid and carbohydrate efficiency ratio) and survival rate significantly improved in crayfish fed OMWW-enriched diets, in a polyphenol concentration-related manner. The activities of the oxidative enzymes GP, GR and CA were evaluated in the hepatopancreas. GP activity did not statistically changed. The increase in GR activity was statistically significant only in the OMWW-HC group. The increase in CA activity was statistically significant in both OMWW-LC and OMWW-HC groups. The immunological parameters (total haemocytes, phenoloxidase activity) significantly increased in OMWW-LC and OMWW-HC groups with respect to the control group. Superoxide anion production in the hemocytes statistically decreased only in the OMWW-HC group. No pathological changes in the midgut and hindgut after OMWW-enriched diets were detected by histological analysis. In crayfish fed on OMWW-enriched diet, total intestinal microbiota decreased, with the exception of anaerobes and yeasts. A significant increase in PUFA and decrease in MUFA was registered in the hepatopancreas. The emerging picture indicates that diets enriched with polyphenols extracted from OMWW had beneficial effects on crayfish growth and health and hence could be successfully employed in aquaculture and considered as a novel strategy of development to the feed industry sector. (C) 2017 Elsevier B.V. All rights reserved.