For fish farmers, uniformity of growth and body size is one of the key traits to be improved in future breeding programs. In domestic Nile Tilapia size differences among individuals are very large but the genetic background of this variability is almost entirely unknown. In a new study, published by Genetics Selection Evolution, researchers of Wageningen UR found that variability of harvest weight and body size traits in Nile tilapia has a substantial genetic component.
Variability of a trait can have a negative impact on production performance, both in livestock and aquaculture. Reducing variability by means of genetic selection has been a long-standing desire in animal breeding. For fish farmer, selection for uniformity of body weight or size could lead to increased profit by producing more fish in the size range that is favoured by the consumers. Moreover, from the point of view of animal welfare, uniformity of fish body weight and size could reduce competition, and thus possible stress, injuries, and mortality.
Selection for more uniform individuals requires that variability of a trait has a genetic basis i.e. that there is genetic variation in residual variance. In this case, within a population, some animals will be less prone than others to phenotypic changes in response to small environmental fluctuations, and thus will have a more stable performance.
Different methods can be employed to study variability of traits. In the current study, researchers used novel approach known as double hierarchical generalized linear models (DHGLM) to quantify genetic variation in uniformity of harvest weight and body size traits (length, depth, and width) in Tilapia. The results showed that residual variance of harvest weight could be reduced by 58% with one generation of selection, while the reduction in phenotypic variance of harvest weight would be 36%. Similar results have been obtained for body size traits.
Selection for uniformity has never been performed in aquaculture species, however results of this and other studies on aquaculture species suggest that aquaculture populations are suitable to validate the estimated genetic parameters by a selection experiment.
The research was done in collaboration with Swedish University of Agricultural Sciences (SLU) and WorldFish, and was sponsored by the EU within the framework of the Erasmus-Mundus joint doctorate programme “EGS-ABG”.