Genetic trends in growth, sexual maturity and skeletal deformations, and rate of inbreeding in a breeding programme for rainbow trout (Oncorhynchus mykiss).
Progress in the Finnish breeding programme for rainbow trout was assessed by estimating genetic trends in growth, maturity age and skeletal deformations and by calculating rates of inbreeding and additive genetic relationships. The analysis included two pedigreed populations with three generations and over 117,000 individuals recorded for skeletal deformations, growth and age at maturity. Because the breeding station is located in fresh water but sea is the main production environment, each family was split into subgroups to be tested for performance either in fresh or sea water. Estimation of breeding values across the generations showed that multitrait selection has produced an average of 7% genetic gain per generation in fresh and sea water growth of market-sized fish. In the population with high frequency of early maturing males, phenotypic culling of early maturing males has prevented an increase in the frequency of early maturing fish. In the other population, the frequency of early maturing females has increased, the genetic change being unfavourable. Weak favourable or no correlated genetic changes were observed in the frequency of deformations in response to selection for the production traits. Rate of inbreeding has remained low, the maximum value being 0.7% per generation. Because mating of close relatives has been avoided, an increase in coefficient of additive genetic relationships describes the risk of the programme more realistically than rate of inbreeding. The average increase in relationship was 0.7% per generation, a value below the suggested precaution level.