Compared with the growth of juvenile Atlantic salmon there are some differences in the mechanisms of juvenile brown trout growth in waters of the north of European Russia. The growth rate of juvenile brown trout is considerably higher than that of juvenile Atlantic salmon. As opposed to juvenile Atlantic salmon it often happens among brown trout parr that older individuals turn out to be appreciably smaller in size and weight than younger individuals. According to our data the growth rate of brown trout is primarily controlled by the climatic, hydrological and feeding conditions rather than by the geographical location as in the case of Atlantic salmon.