Intraspecific inbreeding and line-breeding of N1 and N2 strains in Nile tilapia (Oreochromis niloticus), and their interspecific outbreeding with A strain of blue tilapia (Oreochromis aureus) were conducted. The experimental fishes were all from the conserved stocks at Freshwater Aquaculture Research Center, FRI. After 364-day culturing period, the results showed that progeny of N2 × N2 had the best growth performance, and those of N1 × N1 had the worst. Their average weight gain (WG) were 2.5 and 1.5 g/day, respectively. The WG of progeny from N1 × N2 and N2 × N1 were 2.0 and 2.2 g/day, respectively. Progeny of female N1 × male A and female N2 × male A were all males that indicated genetic purity of Nile and blue tilapia kept in the Center was high. The growth performance of progeny of N2 × A was also high, second to that of N2 × N2. Due to all male progeny, the study suggested that N2 × A might be extended to fish farmers.