Population parameters of Oreochromis niloticus, introduced in Lake Toho in 1995, were investigated using the FiSAT software. Data was collected monthly from January to December 2007. Total length of 1047 specimens ranged from 4.1 to 40.2 cm. The growth parameter K was estimated to 0.33 year–1 with asymptotic length L∞= 41.5 cm. The recruitment pattern was continuous year-round with one peak (May-July). The total (Z), natural (M) and fishing (F) mortalities were 1.10 year–1, 0.74 year–1 and 0.36 year–1 respectively. The Z/K ratio was 3.7, the exploitation rate (E) 0.33 and the relative yield/biomass per recruit Emax 0.65. The fishing effort is slow with a dominance of small size individuals in the captures. There is growth-overfishing and an increase in the mesh size of fishing gears should go along with that of fishing effort to preserve the population on the species.