An advantage of aquaculture farming compared with fisheries is that it is possible to genetically improve economically important traits through selective breeding. This is possible because many traits have underlying heritable genetic components and individuals carrying those desirable traits can be selected as the parents of the next generation. A difficulty however, is how to measure the quality traits on the potential breeders. Traditionally, measuring the traits on relatives like full- and half-sibs have been applied. However, with new technologies such as near-infrared reflectance spectroscopy, X-ray tomography (CT) and Fotofish, it is now possible to measure fat% and filet color with high precision. Furthermore, new technological advances have opened new doors to potentially estimate fat% and filet color on live animals. Improving fat% by selective breeding is possible, as the heritability of the trait is relatively high (h2 = 0.25) and a genetic gain of 4 % per generation has been reported for rainbow trout. On the other hand, the heritability for flesh color shows high variation, but it is particularly high when measured using CT (h2 = 0.47). Finally, fillet yield has a rather low heritability (h2 = 0.16) and reported genetic gain per generation is close to zero.