| Abstract | In the present investigation, spirulina (Arthrospira fusiformis) was used as feed additives on growth performance in Nile Tilapia (Oreochromis niloticus). A. fusiformis was isolated from various rook pool of a rocky shore, Alexandria and Kafr El-Sheikh Governorates, Egypt. The results showed that the optimum medium, pH and temperature for the growth protein and chlorophyll-a content of A. fusiformis were Zarrouk medium, 9 and 35°C, respectively. The dry weight of A. fusiformis was 1.8 g/L and protein and chlorophyll-a contents were 64.3% and 13.2 mg/g at 35°C and pH 9, respectively. A. fusiformis was used as feed additives on growth performance in Nile Tilapia for 12 weeks. Three (3) diets were formulated to be isocaloric and isonitrogenous containing (about 4616 kcal/kg DM) and (about 31.49% CP) for Tilapia fingerlings: one, a control diet without supplements; second, a supplement with 1% A. fusiformis and third, a supplement with 1% Spirulina pacifica. Results indicated that fish fed on 1% spirulina exhibited greater growth than those fed with the control diet. Fish fed with the control diet had the lowest protein content. Carcass lipid recorded the highest value in the control treatment, which was statistically different from the supplemented treatments. Ash content increased significantly with the increase spirulina levels as compared with the control treatments. Fish fed with spirulina-containing exhibited higher glucose, lipid and protein values in fish serum. Also, fish fed with spirulina-supplementation significantly decreased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) values compared with control suggesting that spirulina is an appropriate growth-stimulating additive in Nile Tilapia culture |