Abstract
A fully pedigreed population based on the sixth generation of GIFT (Genetically Improved Farmed Tilapia) was established in Malaysia in 2002. Progeny were generated in two spawning seasons, 2002 and 2003. A number of statistical models were fitted to the data collected throughout the study, either to estimate breeding values (EBVs), variance components, or response to selection. Parents used in the spawning season of 2003 were either selected as having high estimated breeding values for live weight (LW) at approx. 7 months of age, or as having EBVs as close as possible to the average. In this way Selection and a Control lines were created, respectively. Two production environments were used to grow-out the progeny. At approx. 7 months of age females' live weight was 84% that of males, whereas live weight in cages was 83% of that in ponds. The heritability estimated from the animal variance component was 0.34 (s.e. 0.069), whereas the maternal and common environment effect estimated from the dam variance component was 0.15 (s.e. 0.031). Response to selection was estimated by three methods: (i) Comparing the least squares means of LW for the Selection and Control lines in the progeny of the 2003 spawning season, (ii) Comparing the estimated breeding values for LW between the progeny of the 2002 spawning season and those of the Selected line in the 2003 spawning season, and (iii) Comparing the estimated breeding values of the Selection and Control lines in progeny of the 2003 spawning season, respectively. Expressed as a percentage of the overall least squares mean for LW in the population, the estimates were 8.4, 8.7 and 11.4 for methods (i), (ii) and (iii), respectively. The results are discussed in relation to other work. It was concluded that there was still additive genetic variance in the GIFT population established in Malaysia, and that it was capable of further response to selection.
Published Version
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