Genetic improvement of Nile tilapia (Oreochromis niloticus) with special reference to the work conducted by the WorldFish Center with the GIFT strain

We mainly (but not exclusively) draw on research and development work carried out by The WorldFish Center (WorldFish). We review in detail the current state of development of a selection program that has had a main focus on growth rate and body traits. We also present some new, unpublished, information. There is evidence of sustained gains of 10–15% per generation over more than six generations. To date, these gains have not been accompanied by any undesirable correlated response. However, the prospects of altering sexual dimorphism and the shape of the fish appear to be very limited. We also examine the issue of an appropriate environment for selection. Not surprisingly, experimental evidence on genotype by environment interactions suggests that this is more likely to be of importance when the environments in question are markedly dissimilar. We argue that no universal guidelines can be prescribed with regard to the need for more than one selection program to cope with different production environments, but rather, each case should be examined in its own right. Finally, we discuss traits likely to be candidates for inclusion in future, more elaborate, breeding objectives for Nile tilapia (Oreochromis niloticus), comment on selection methods that may be implemented in the future and conclude by stressing the need to maintain an effective population size in selection lines to ensure their sustainability over time.