Search

Effects of family differences on survival, length, weight, growth, and pyloric caeca number for juvenile rainbow trout Oncorhynchus mykiss were analyzed in binary associations of families (sib-groups), using a genetic variant with “golden” phenotype as a marker. In such an association, the performance of a family i mixed with family j depends on its own ability (P1), on the influence of the associated family (AJ), and on possible effects specific to the ij association. Experimental results showed that specific effects were negligible, and that the AJ influence was significant on body length and weight (after 3 mo of age), and opposite to the PJ value of the same family. Growth showed the same feature, but short of significance. The genetic marker caused some detrimental pleiotropic effects on length, weight, and growth, and some limited interactions with the familial factors studied. Results suggest that, when practicing selection, aquaculturists should prevent early size differences from becoming enhanced by competition, and should consider periodic size grading and multi-step selection. Results also suggest that family interactions should be accounted for when analyzing mixed-family genetic evaluation data.

The variability of parental origin in hatching and early survival rates of brown trout ♀ × brook trout ♂ hybrids was estimated, using factorial breeding plans, and monospecific control samples from each dam. Evidence was obtained of: • - sire effects bearing on eggs and alevins • - low sire × dam interaction effects • - important dam effects, some of which bear on eggs and are strongly correlated to those measured from control lots, while the other, uncorrelated effects, are observed on alevin survival. From these results it is concluded that genetic investigations of parental differences, especially maternal ones, operating on progeny survival should lead to improvement of hybridization techniques.

Two sires were selected, from each of four full-sib families, according to high (“sup”) and low (“inf”) caeca number. Pyloric caeca number, precocity and growth of offspring were studied in a factorial breeding plan of these eight sires crossbred with three dams. Compared with the progeny of sires “inf”, the progeny of sires “sup” exhibited (a) a higher caeca number, (b) slightly more precocious development (as shown by beginning of hatching, first feeding and degree of hydration during yolk resorption) and (c) a higher growth rate. Significant correlations were found, within dams, between fish length at 239 days and caeca number both within and between families of offspring. Although the physiological links between caeca number and growth are still obscure, the possibility of improving growth performance in rainbow trout by indirect selection on caeca number is discussed.