Abstract Limited efforts have been made to study the genotoxic effects of ammonia in cultured
OOreochromi niloticus. Therefore, the present study was planned to assess the genotoxic effect of
ammonia in cultured O. niloticususing random amplified polymorphic DNA (RAPD) assay. Fish
was categorized into four groups. The 1st group exposed to 2.5 mg/L of total ammonia nitrogen
(TAN) (0.16 NH3 mg/L), the 2nd exposed to 5.0 mg/L of total ammonia nitrogen (TAN) (0.32
NH3mg/L) and the 3rd exposed to 10.0 mg/L of total ammonia nitrogen (TAN) (0.65 NH3
mg/
L), in addition to control group for the treatment period of 6 days. The results revealed that some
genes inO. niloticusare susceptible to DNA disturbances/mutation as a result of exposure to high
concentration of ammonia in water, this clearly indicated using RAPD screening assay.