The current evaluation was done for determination of the efficacy of the dietary supplementation of chlorella vulgaris ethanolic extract on the various indices of growth performance, some biochemical parameters of blood, lysozymal activity, digestive enzymes activity as well as survivability of common carp (Cyprinus carpio) fish infected with E. tarda challenge. Where about 150 carps (70±3 g), were divided at randomly into 5 experimental groups in triplicate, Gp1: negative-control. Gp2: infected control, carps fed control diet for 40 days then challenged with IP injection with (1x107 CFU ml-1) of E. tarda strain. Gp3: carps fed supplemented diet with 0.1 g/ kg chlorella extract for 40 days then challenged. Gp4: carps were fed supplemented diet with 0.2 g/ kg chlorella extract for 40 days then challenged. Gp5: carps were fed a commercial control diet and challenged at the day 40 then treated with oxytetracycline with a dose (55mg/kg of fish body weight) for 10 days. After 40 days of supplementation, an improved growth indices were observed in the supplemented groups especially Gp4. Total protein, albumin, globulin, lipase and amylase activities were significantly increased in all supplemented groups compared with the control, moreover lysozymal activity were increased in these groups throughout the experimental period. There is no a significant difference in levels of ALP, ALT, AST, creatinine, and Urea were recorded in supplemented groups and the normal levels of Gp1. The survivability of carps challenged with E. tarda was elevated from 53.3% at Gp2 up to 90, 86.6 and 80% at Gp5, Gp4 and Gp3 respectively.
So chlorella vulgaris extract is considered an optimal choice for dietry supplementation in fish farming for enhancement of growth rate, immunological status, disease resistance capability and survivability.