Effects of Liquid Culture Chlorella vulgaris Diet Supplementation on Growth and Oxidative Status of Common Carp ( Cyprinus carpio )

Microalgae are receiving increasing attention in aquaculture research because of their high protein levels, nutrients and bioactive compounds with functional properties. The objective of the present study was to assess the potential of liquid Chlorella vulgaris (LCV) as carp ( Cyprinus carpio ) feed additive and its effect on growth performance, feed utilization, flesh proximate composition, haematological parameters and oxidative status. The algal biomass, produced in a culture medium of 90% recirculating aquaculture system wastewater and 10% Tamia medium, reached 1.05 g L −1 dried residue and contained 48% protein, 14.5% lipids and 19.2% carbohydrates. The essential amino acid profile was rich in lysine (9.9 g × 100 g −1 DW). It also contained 10.22 mg g −1 DW chlorophyll a and 646 µg g −1 DW total carotenoids. Juvenile fish (11.39 ± 0.84 g initial body weight and 7.69 ± 0.66 cm standard length) received four experimental diets for 12 weeks: a control diet and three diets supplemented with LCV at inclusion levels of 5%, 10% and 15%. A positive linear growth trend was observed in fish receiving liquid algal supplementation. Final body weight ( p < 0.001), weight gain ( p < 0.001), specific growth rate ( p = 0.022), relative growth rate ( p < 0.001) and feed conversion ratio showed positive trends in the 10% and 15% groups. No significant changes were detected in, condition factor, hepatosomatic index or viscerosomatic index. The algal‐based diets influenced the proximate composition of carp flesh. Haematological analysis showed increases in, erythrocyte numbers, haemoglobin concentration and thrombocyte levels at higher inclusion rates ( p < 0.001). Antioxidant response was enhanced, with higher superoxide dismutase, catalase and glutathione peroxidase activities. Overall, dietary supplementation with LCV can improve growth performance, feed efficiency, redox balance through enhanced antioxidant status, and hematological condition in common carp, highlighting its value as a novel functional feed additive for carp aquaculture.