In the present study, the effects of polyphenols extracted fromolive millwastewaters (OMWW)were investigat- ed in the narrow clawed Astacus leptodactylus in a 24 week-feeding trial. 0.5 and 5.0 g of OMWWpolyphenolic extract were mixed with 1 kg of basic diet to generateOMWW-LC (Low Concentration) diet andOMWW-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 fedOMWW-enriched diets, in a polyphenol concentration-relatedmanner. The activities of the oxidative enzymes GP,GR and CAwere evaluated in the hepatopancreas. GP activity did not statistically changed. The increase in GR activitywas statis- tically significant only in the OMWW-HC group. The increase in CA activity was statistically significant in both OMWW-LC andOMWW-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 productionin the hemocytes statisticallydecreased only in theOMWW-HCgroup.No pathological changes in the midgut and hindgut afterOMWW-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 sig- nificant increase in PUFA and decrease inMUFAwas registered in the hepatopancreas. The emerging picture in- dicates that diets enriched with polyphenols extracted fromOMWWhad beneficial effects on crayfish growth and health and hence could be successfullyemployed in aquaculture and considered as a novel strategy of devel- opment to the feed industry sector.

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