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Genetic parameters and realized response to selection for harvest body weight were obtained for the F5 generation of O. shiranus during on-farm growth testing in Chingale, Zomba, Malawi. Two lines of fish, the selected and control were used for the experiment. The selected line was produced through single pair mating of F4 broodstock in 1 x 1 m3 hapas. The broodstock was selected using combined family and within family selection. There were 17 males and 51 females that were mated using a hierarchical design. The full-sib families were reared separately for 90 days before PIT tagging and growth performance testing in 10 common ponds that were owned by 10 fish farmers. The control line was produced through on-farm mass spawning of F4 broodstock whose mean breeding values were around the mean. The realized genetic gain was estimated as the difference in the least squares mean of the selected and control lines expressed as a percentage of the base population least squares mean. The heritability value was 0.30 but was accompanied by a large full-sib family effect of 0.26. The realized genetic gain over the five generations of selection was 37.8% representing 7.6% per generation. The selected lines showed higher (10%) survival from the control lines. The results are discussed in relation to the importance of on-farm genetic selection for small scale farmers and the sustainability of the breeding program.
