The present study investigated effects of transgenic Synechocystis sp.PCC6803 containing flounder GH gene as feed additive on blood physiological and biochemical indices and peripheral blood erythrocyte micronucleus and other nuclear abnormality using juvenile turbot cultured in lab and in fish farm.Results showed that transgenic Synechocystis had no influence on blood cell count

haemoglobin content and mean corpuscular volume（p>0.05）. 1.0% additive dosage of transgenic alga caused no increase in activities of aminotransferases

alkaline phosphatase and lactate dehydrogenase in serum（p>0.05）.No significant differences（p>0.05） were observed between experimental and control group in total protein

glucose

triglyceride

cholesterol

urea nitrogen

creatinine levels

and sodium

potassium

chloride and phosphorus concentrations（p>0.05）.Feeding transgenic Synechocystis did not induce the formation of micronucleus and other nuclear abnormalities in erythrocyte.Results of the present study indicate that transgenic Synechocystis can not impair organs of turbot and has no genotoxic effect on the fish

it is a safe transgenic feed additive and can be used as growth promoter for turbot.