Abstract—The potential for Tilapia zillii and Oreochromis urolepis urolepis culture in seawater was evaluated by determining their survival and growth in seawater at 35‰. Fingerlings were collected from Pangani River using seine nets and reared in 1 m3 concrete ponds after acclimatization from salinity of 2‰ to 35‰. Fingerlings were also reared in freshwater as controls. Fingerlings were fed twice daily using commercial fish feeds (White Rose floating pellets), initially at a rate of 5% of their total body weight (TBW) and 10% of their TBW after two weeks. Their growth rate (length and weight) was recorded weekly except controls for handling, their growth being recorded at the beginning and end of the experiment. The average weight gain (g.week-1), percentage weights gain (week-1) and specific growth rate (SGR, %.day-1) were determined in freshwater and seawater. There was no significance difference (p >0.05) in the SGR between the two species in seawater. The survival rates of O. urolepis urolepis were 100% in freshwater and seawater and 89% and 96% respectively for T. zillii. This study showed that T. zillii and O. urolepis urolepis can survive and grow in seawater but the former is a better candidate for mariculture