Brown trout in Lake Femund migrated from the nursery streams mainly at 2 years old, but ranging between 1 and 8 years. Brown trout switched to piscivory from 3 years onwards, and a body length of 17·5 cm, according to back calculation from scales. Fast growers switched to piscivory at a younger age and smaller size than slow growers. The most slow-growing trout switched to fish feeding at 9 years old and a mean body length of 36 cm. The growth of the invertebrate feeders was almost rectilinear to c. 45 cm and 11 years of age. Switching to a fish diet induced increased growth rates. Age at sexual maturity increased with the age at which the fish became piscivorous. The invertebrate feeders matured at an age similar to that of the most fast growing piscivorous trout. The mortality rate of sub-adults and adults did not differ significantly between fish and invertebrate feeding trout. Longevity of piscivorous trout was estimated at 11 years and of invertebrate feeders at 10 years.