A complete diallel cross experiment was carried out with eight strains of Nile tilapia
. Oreochromis niloticus . The strains represented four wild populations collected from various
locations in Africa and four populations that had been reproduced over a large number of
generations for tilapia farming in Asia. Growth performance was recorded in a total of 23 739
individually tagged progeny of the 64 different strain combinations after a grow-out period of
about 90 days in seven different test environments representing applied farming systems in the
Philippines. Least square means of body weight at harvest were computed for each strain
combination within and across test environments, and additive genetic effects, maternal recipro-
cal effects and non-additive genetic effects heterosis were estimated. The least square mean . .
heterosis of both reciprocals of all strain crosses across all test environments was 4.3%, and the
cross that expressed the largest non-additive genetic effect showed a least square mean heterosis