A genetic analysis of body weight and length in rainbow trout reared in seawater for 18 months

Abstract

Data from four year-classes of raibow trout was analysed. The brood fish originally came from different Norwegian fish farms, but all are considered to belong to the same population. During the freshwater period each full-sib family was reared separately and each group was given as equal environmental conditions as possible. Fingerlings from each fullsib family were sampled and freeze-branded. At an age of one year fingerlings from each family were sampled and transported to different fish farms along the Norwegian coast. This paper deals with the traits body weight and length at slaughter after about 18 months in net cages in the sea. Fish farm × sire interaction was significant, but accounted for a relatively small part of the total phenotypic variance. It is concluded that genotype × farm interaction can be ignored when planning a selection programme for rainbow trout under Norwegian farming conditions. A significant interaction was found between sire and dam, implying the presence of non-additive genetic variation. The heritabilities for body weight and length estimated from sire components (year-class 1973, 1974 and 1975) were 0.17 and 0.23, respectively. The genetic correlation between body weight and length was close to unity. Genetic variation in body weight of rainbow trout is high, about three times as high as for body length. The heritabilities estimated for condition factor were small and none of the sire components were significant. It is concluded that the combination of weight and length used to calculate the K-factor has little genetic basis.