Aquaculture RESPONSE TO SELECTION IN TWO PRODUCTION ENVIRONMENTS IN THE GIFT STRAIN OF NILE TILAPIA (OREOCHROMIS NILOTICUS)

SUMMARY Progeny were generated in two spawning seasons (2002 and 2003) in a fully pedigreed population based on the sixth generation of GIFT (Genetically Improved Farmed Tilapia) established in Malaysia. Two lines were created (Selection and Control), and two production environments (cages and ponds) were used to grow out the fish. Live weight at harvest (LW) was the trait under selection, treating the production environments as a fixed effect in the model. In the analysis presented here LW in cages and in ponds was treated as two different traits (LWC and LWP, respectively). For LWC, expressed as a percentage of the overall least squares mean in the population, the estimates were 9.2, 9.6 and 12.7 for methods (i), (ii) and (iii), whereas for LWP they were 8.2, 7.9 and 10.4, respectively. It was concluded that selection response was being achieved in both environments and that there was not enough evidence to justify the conduct of separate genetic improvement programs for cage and pond environments