Comparative life-history characteristics of native and hatchery-reared brown trout, Salmo trutta L., in a sub-Alpine reservoir

Wild and non-native hatchery-reared brown trout, Salmo trutta L., released when 2 summers old, were caught in the littoral habitat of Vinstervatna Res ervoir, southern Norway. Hatchery-reared brown trout grew more slowly and h ad a smaller asymptotic length (293 +/- 71 mm CL) than native fish (391 +/- 56 mm CL). Hatchery-reared brown trout also exhibited significantly shorte r life spans than native fish. This category consisted mainly of individual s aged 2+ and 3+ years, and only 1.5% of the specimens were aged greater th an or equal to 5 years. The ages of the native fish in the sample were betw een 2 and 8 years, and the most abundant age groups of trout were 4+ and 5 years. It is suggested that the differences in life-history characteristic s are related to adaptations by the native trout to the local environmental conditions. In this reservoir, which has a limited food supply as a result of water level fluctuations and a high level of inter- and intraspecific c ompetition, environmental effects might be significant.