The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout (Salmo truttaL.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m2and 18.6 g/m2in the 2 year