Color Assessment of Experimentally Pigmented Rainbow Trout

The development of color in the muscle of pen‐reared rainbow trout, Salmo gairdneri, resulted from the absorption and deposition of astaxanthin introduced into the diet. The degree of coloration compared to that of control fish, fed diets naturally low in pigment, was easily evaluated visually. The major change in reflectance characteristics on increased pigmentation involved increase in light absorption at shorter wavelengths (astaxanthin absorption maximum ca. 490–500 nm) manifested by decreased CIE Z and increase in excitation purity Pe. Indeed, either Z or Pe alone ranked samples in close agreement with visual scores. No other single colorimetric quantity in any of the Jour systems studied shared this property. To relate colorimetric measurements in Hunter L a b, CIELUV, and CIELAB to visual scores, one had to resort to multiple‐regression analysis. This increased the complexity of the analysis without offering any advantage. Pigment concentration alone cannot be used as a criterion of perceived coloration. Both reflectance measurements and visual appearance were profoundly affected by differences in properties of the light‐scattering cellular matrix at constant pigment concentration.