Estimates of the strain additive, maternal and heterosis genetic effects for harvest body weight of an F2 generation of Oreochromis shiranus

Estimates of the strain additive and maternal genetic effects, and the strain individual, maternal and paternal heterosis effects were obtained for harvest body weight of an F2 generation of Oreochromis shiranus in Malawi. The F2 generation was a composite population that was formed from selected offspring of a complete diallel cross (F1 base population) between four wild strains; i.e. from the Shire River and from lakes Malawi, Chilwa and Chiuta. Harvest body weight was recorded on 1326 individually tagged fish from 52 full-sib families; i.e. the offspring from 33 sires and 52 dams. The full-sib families were reared in 1 m3 tanks for 76 to 131 days before tagging. The tagged fish were tested for growth for 180 days in mass grow-out ponds at three farm environments representing the different climatic conditions of the country. Across the farm environments, the mean performance of the purebreds and crossbreds was 81.0 ± 2.0 g and 73.9 ± 1.9 g, respectively, thus giving a negative average heterosis of − 8.8%. Of the strain genetic effects, the strain maternal heterosis effect was the most important followed by the strain additive genetic, strain individual heterosis and strain maternal genetic effects. The strain paternal heterosis effect was not significantly different from zero (P > 0.05). The animal additive genetic effect was more important than the other genetic effects. The Shire strain ranked highest for the strain additive genetic effect, while the Nkhotakota strain dams ranked highest for the strain maternal genetic effect. The Chilwa, Chiuta and Nkhotakota strain dams when mated with the Shire sires ranked high on strain maternal heterosis effect. The correlation between the strain additive genetic performance and the strain total performance was positive and relatively high (r = 0.75). The results are discussed with respect to selection strategy to improve the performance of the species in Malawi.