Effect of inbreeding on body weight at harvest in rainbow trout, Oncorhynchus mykiss

Sammendrag

Three nucleus breeding populations of rainbow trout (Oncorhynchus mykiss) under selection for six generations were investigated for the effect of inbreeding on body weight at harvest. The coefficients of inbreeding for each individual were estimated from complete pedigree information starting at base generation zero. For each population within generation, inbreeding effect was estimated using a fixed linear model and a sire-dam mixed additive genetic model. Estimates of inbreeding effect per generation vary due to the different distributions of inbreeding coefficients in each generation. The magnitude of inbreeding effect for each population across generations were estimated using a fixed linear model and three sire-dam mixed models: additive (A), additive plus dominance (A + D), and additive plus dominance plus additive by additive epistasis (A + D + A x A) with the inbreeding coefficient, F as covariate. The estimates of inbreeding effect from the fixed linear model were substantially lower than those from the sire-dam mixed models for all populations. The models (A + D) and (A + D + A x A) exhibited quite similar estimates of inbreeding effect, which were substantially higher than the (A) model. The results suggest that addition of the additive by additive genetic effect in the (A + D) model does not have a significant outcome on the estimation of inbreeding effect because additive by additive genetic interaction may not be important for growth. For unbiased estimation of inbreeding effect, the (A + D) model with F as a covariate may be sufficient. The inbreeding effect on body weight at harvest calculated as the average of the estimates obtained from models A + D and A + D + A x A, were -1.6, -5.0, and -4.5% per 10% unit increase in inbreeding coefficients for populations 1, 2, and 3, respectively. These values meant body weight at harvest was moderately affected by inbreeding but were not high enough to cause any serious impact in the selective breeding program for rainbow trout in Norway. This implies that maintenance of moderate effective population size per generation and following a strict mating policy for breeders selected as parents for future generations could delay the accumulation of inbreeding and minimize its effect on growth. (C) 2001 Elsevier Science B.V. All rights reserved.