Reprint of: Genetic parameters of in-vivo prediction of carcass, head and fillet yields by internal ultrasound and 2D external imagery in large rainbow trout (Oncorhynchus mykiss)

Abstract

Selection to improve processing yields relies on sib selection, in which live candidates are ranked according to their family breeding value. This approach limits genetic progress, as it only exploits genetic variability between families and not within them. Indirect criteria measured on live candidates could overcome this limitation. The present study (I) proposes a procedure to identify indirect criteria to predict processing yields in rainbow trout (head, carcass and fillet yields), (2) estimates genetic parameters of these indirect criteria, and (3) predicts relative genetic gains in processing yields using full-sib selection or indirect individual selection on those indirect criteria. DNA-pedigreed all-female rainbow trout Oncorhynchus mykiss (n = 2029, 1631.0 +/- 355.6 g) from 600 families produced from 100 sires and 60 dams were characterized by external and internal non-lethal morphological measures using digital pictures and real time ultrasound tomography. Nineteen landmarks were recorded on the digital pictures to define the outline of the body, head and lateral line. Their coordinates were used to calculate different lengths, heights and areas. Five different internal thicknesses were measured by ultrasound tomography. In the first phase of this study, processing yields were predicted using multiple linear regressions including both external and internal morphometric variables. In a second phase, the heritability of the predicted values and their genetic correlations with real processing yields were estimated using animal models. Predicted yields exhibited intermediate heritabilities (0.25-0.28) that were half the value of heritabilities for real processing yields (0.47-0.55), but had high genetic correlations with these real yields (0.87-0.90). The relative efficiency of indirect selection (IS) on these indirect criteria was compared to theoretical mass selection (MS) or sib selection (FS) with different family sizes (10 or 100) and two different selection pressures (10% or 40%). At the same selection pressure (10%, with 100 sibs per family %), full-sib selection created genetic progress 49.6% to 60.5% higher than indirect selection according to the processing yield targeted. However, when sib-selection pressure was limited to a more realistic between family selection pressure (40% and 10 sibs per family), indirect selection with 10% selection pressure was 21.9% to 32.7% more efficient than sib selection.