Body traits in rainbow trout: I. Phenotypic means and standard deviations and sex effects

Abstract

Data recorded at slaughter on 2–4-kg rainbow trout ( Salmo gairdneri) from three year-classes were analysed. The following traits were recorded for all fish: ungutted and gutted body weight; body lenght; dressing percentage; condition factor; gonad weight and gonad index; belly thickness, scored and measured; abdominal fat score, viscera weight and viscera index; and meat colour score. The following traits were recorded for a sample of the fish from each year class: body circumference at the pelvic, dorsal and anal fins; area of the cross sections at the pelvic and dorsal fins; two belly thickness traits measured on each cross section; total height, height and width of each cross section; water, fat and protein percentages in the meat of the cross section at the dorsal fin; three body shape traits; and five cross section shape traits. The means and standard deviations for most traits were very similar across year-classes. The phenotypic variation was high for body weight, belly thickness, abdominal fat and percent water and fat in the meat. The variation was also substantial for meat colour score, condition factor and for most of the shape traits. Except for gonad weight, gonad index and viscera weight, sex effects accounted for a small proportion of the total variance, but were significant for most traits and should be taken into account in making a model. The few significant sex-by-year-class interaction effects were negligible. As high selection intensity can be practised in this species, the possibilities for genetic improvement of most of the examined traits are very good, on the assumption that the traits also show genetic variation.