In January 2015, Hooi Ling Khaw defended her PhD-thesis entitled “Cooperative and Uniform Fish? Social interactions and variability in live body weight in the GIFT strain in Malaysia.” In this thesis, Hooi Ling investigated genetic and environmental interactions in Nile tilapia, and their effects on growth rate and body weight. Competitive behaviour seems to go along with more variation in body weight, but does that mean that we can improve growth rate by breeding more cooperative uniform fish?
Tilapia is the most widely cultured aquaculture species in the world, and Nile tilapia accounts for ~70% of the global tilapia production. Tilapia are produced both in cage and pond systems, which may create genotype by environment interaction, where different genotypes respond to environments in different ways. Hooi Ling’s research shows that the genetic correlation for body weight and size between both systems is high (~0.8), so that a single breeding program can be used for both production systems. Her research also demonstrates that tilapia show competitive interactions, which have a genetic background. Those social effects contribute substantially to heritable variation in body weight, indicating that breeders can improve growth rate by breeding fish that are less competitive.
Competition is related to variation in body weight among individuals; greater competition generally goes together with greater variation among individuals. Therefore it was also investigated whether variability in body weight is heritable, which would allow to breed for better uniformity. Results show that uniformity in tilapia has substantial heritable variation, but this variation seems unrelated to competition among individuals. Thus uniformity can be improved by genetic selection, but this does not necessarily lead to cooperative fish.