The main objective of this paper was to report more reliable estimates of the genetic variation and the genotype by test environment interaction for harvest body weight in the GIFT population in the Philippines than could be obtained from the base population by using the data from the five generations following the base population and that covers a wider span of test environments than the later experiments referred to above. Included are also estimates of the genotype by sex interactions for body weight. The importance of the latter is to investigate to what degree the expression of growth in both sexes is determined by different genes and thus should be treated as different traits in a breeding program, in particular since monosex culture is widespread in Nile tilapia.