Oreochromis esculentus (Graham, 1929) is endemic to the Victoria and Kyoga lake basins. It was the most important commercial fish species not until the introduction of gill-nets (1905 to 1916), that it declined and became very rare in the main water bodies of lakes Victoria and Kyoga. However, some populations appeared to have survived in some minor lakes in these basins which form valuable reservoirs for the species and could be used in restocking of the main lakes.
Data were collected on the population characteristics of 0. esculentus in lakes Kachera, Kayanja, Mburo and Kayugi in the Victoria lake basin and lakes Lemwa and Kawi in the Kyoga lake basin from December 1997 to June 1999 through experimental fishing and examination of commercial catches. The aspects examined included species composition, relative abundance, the distribution and length frequency distribution of 0. esculentus. Biological characteristics included lengthJweight and condition factor, the food, size at first maturity, sex ratio, and fecundity of 0. esculentus. The results were compared among lakes and with the available historical data for lakes Victoria and Kyoga.