Selecting Sole: breeding programs for natural - mating populations

The aim of this thesis was to design a breeding program for increased productivity of farmed common sole, Solea solea, 1) using natural mating in groups to obtain offspring and 2) using present farm infrastructures as much as possible. Parental allocation with DNA marker data on offspring from natural mating parents showed that parental contributions were highly skewed. This indicates that few animals contribute to majority of the offspring. Levels of coancestry in offspring populations were high (2-4%) showing that selection methods need to restrict rates of inbreeding in future generations. Genetic variances of body weight and body length in common sole were measured at harvest and it was shown that genetic improvement of these traits is possible. It was pointed out that selection on growth of common sole needs to be accompanied by selection for shape to compensate for undesired correlated responses in shape. Further, it was demonstrated that in populations with skewed contributions, use of marker data can be more efficient once breeding values are estimated with continuous molecular relatedness rather than with a reconstructed pedigree. To decrease costs of breeding programs, selection of parents may be from production populations directly. Results indicated that estimation of genetic parameters is affected by husbandry practices as grading, but that effects are predictable. To optimise breeding programs with natural mating of parents, 2-stage selection schemes with optimal contribution selection from mass selected and genotyped fractions were compared with mass selection schemes. Using 2-stage selection schemes, rates of inbreeding can be restricted with a smaller nucleus than with mass selection schemes. However, response is lower as well. The different findings in this thesis are put into context of a breeding program for common sole and discussed in relation to profitability, benefits of natural mating and correlated responses to selection for growth.