Abstract: Introductions of better performing tilapia species and development of techniques to manage unwanted reproduction have made significant developments that led to success in tilapia farming. Samples were obtained from three pools at Dirab fish station, in Saudi Arabia. The genomic DNA of fish was extracted from 4 μL of whole blood following the method described by pharmacia Biotech. DNA amplifications were performed by using PCR program consisting: denaturation temperature 94°C for 4 min and 40 cycles consisting: 94°C denaturation for 30 sec, annealing temperature 36°C for 1 min, extending temperature 72°C for 2 min. Out of 12 primers one was selected for PCR reaction using genomic fish as template. The total band profiles of sample fishes from first three pools and that of the second three pools were counted. The similarity index between populations, Oreochromis aureus and Oreochromis mussambicus and Oreochromis niloticus were calculated by using the formula, SI = 3NABC /(NA+NB+NC) where NABC was the total number of RAPD bands shared by individuals A and B, C and NA, NB and NC were the number of bands scored. The mean band profiles of all individuals were also calculated as 8.1 and 8 and the Similarity Index (SI) values between the band profiles of all individuals on the same gel were 1.479 and 1.5.