Captive breeding programs for salmonids are widespread. Evidence that stocking of captivebred fish has negative effects on wild populations has accumulated during the last decades. The mechanisms mediating these negative effects are however largely unknown. This thesis study looked at juvenile brown trout (Salmo trutta) reared in a common hatchery environment but originating from different groups of mothers in order to evaluate genetic influences. By means of parentage assignments fitness of each female broodstock was estimated by calculation of the average survival of each females offspring. Morphology and survival of 511 offspring of wild-reared mothers were compared to 672 offspring of first generation farmed mothers. Traditional and geometric morphometric analyses revealed that they are morphologically differentiated and that these differences are likely of genetic origin. Furthermore shape differences at the beginning of the hatchery-rearing became progressively smaller with time in the hatchery. Wild fish unde1went larger shape changes during the hatchery-rearing than captive fish. The causes for this morphological convergence inside the hatchery are uncertain but only little evidence for selection on morphology was found. The thesis showed that a single generation of captive breeding can generate measurable shape differences and that wild fish morphology becomes more similar to captive fish morphology during hatchery-rearing. These findings highlight that captive breeding programs invoke measurable changes in fish and that their usage for stocking wild populations should therefore be considered carefully.