JKAU: Mar. Sci., Vol. 32 No. 2 pp: 1-12 (2022 A.D.) DOI :10.4197/Mar.32-2.1 1 Effect of Commercial Probiotics on Growth Performance of Sabaki tilapia, Oreochromis spilurus Afnan Ali Ghurab, Mamdouh Al Harbi and Sambhu Chithambaran Faculty of Marine Sciences, King Abdulaziz University, Saudi Arabia Sambhu@kau.edu.sa Abstract. The use of beneficial bacteria to improve fish health and growth is an innovative method in aquaculture practice. A study was conducted to test the efficiency of two commercial probiotics, such as Sanolife Pro-W and Protexin Balance on the microbial load in culture water and growth performance of Sabaki tilapia, Oreochromis spilurus in fiber glass tanks (400 liters) for a period of 75 days. Sanolife was supplied at 3ppm in the rearing water daily, and designated as Treatment 1. Protexin was incorporated at the rate of 1ppm in a supplementary feed, containing 35% protein in diet and considered as treatment 2. A control was also maintained without treating with probiotics in culture water or feed. Healthy and uniform size fish (3.1 ± 0.5g) were stocked at the rate of 25peaces/tank and both treatments and control tanks were set on a randomized design and triplicated. Water quality parameters (physical and chemical), microbial load in water, growth performance and body composition (nutrients) of fish were assessed during the culture period. Significant difference (p<0.01) on growth was observed between control and treatments, the highest growth was recorded in Protexin treated fish. Water quality parameters did not show significant variations. Carcass protein and lipid content showed significant difference between control and treatments. Considerable reduction in bacterial population and improved growth were observed in Sanolife Pro W treated water, when compared to Control. The result shows that Sanolife significantly reduce the bacterial population in culture water and Protexin improves the growth of fish. The outcome of the study has great application in the field of tilapia aquaculture sector in the Kingdom. Keywords: Probiotics, Growth, Microbial population, Sabaki tilapia, O. spilurus. 1. Introduction Aquaculture is one of the fastest growing business among all sectors of agriculture and marine tilapia culture has gained more attention recently in the Kingdom due to its high market demand (Young et al., 2021). The sabaki Tilapia, Oreochromis spilurus is an excellent table fish, has a high salinity tolerance capacity and grows well in sea water salinity up to 45 ppt (FAO, 2015). A major anxiety in intensive culture of tilapia is the increased susceptibility to infectious disease such as Vibriosis and Streptococcosis and various antibiotics and chemicals are being applied in the industry to treat the diseases (Alyssa et al., 2016). It is well accepted that rather than treating a sick fish, it is a better to control the infectious agents in the rearing water (Aly et al., 2008). Fish culturists have shown considerable interests to use non-nutrient dietary additives, immune modulators and probiotics to improve health, growth, or to stimulate immune system function against infectious diseases (Ayyat et al., 2014). With increasing demand for environment friendly aquaculture, the use of probiotics is now widely used in aquaculture practice (Vikash Kumar et al., 2016; Kesselring et al., 2019; Ringo, 2020). The fast and healthy