5 - Tilapia genomic studies

Abstract

Tilapias are now the most important farmed noncyprinid fish globally, with a total production of 4.8 million tonnes in 2013. The bulk (>70%) of the production comes from a single species, the Nile tilapia (Oreochromis niloticus). Most of the world’s tilapia production is from countries outside of their natural range in Africa and the Levant. The genetic status and species composition of farmed tilapia stocks has been complicated because of multiple introductions of different species from Africa, difficulties in species identification, the widespread application of interspecific hybridization, and poor hatchery management that has allowed hybrid introgression in some stocks. This makes it very important to understand the background history of any stock to evaluate its aquaculture potential and to better interpret results from the growing number of genetic and genomic studies conducted on tilapia. This has been shown to be particularly important in the research undertaken to identify the sex-determination system(s) in farmed tilapia. To date work has focused on O. niloticus and shows that sex-determination in this species is complicated with strong evidence for different mechanisms operating in different linkage groups (LG) in different stocks, primarily LG1 and 23 but with additional influences from other LGs and from elevated temperature in some stocks. Cichlid fish have attracted much attention from evolutionary biologists because of the explosive radiation of species observed in the African great lakes. This, added to the aquaculture interest, resulted in O. niloticus being included in the cichlid genome sequencing project.