Differences in growth between offspring of anadromous and freshwater brown trout Salmo trutta.

Individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway was estimated. The juveniles were incubated until hatching at two temperatures (±SD), either 4.4 ± 1.5 °C or 7.1 ± 0.6 °C. Growth rate was estimated during 22 days in August-September when the fish on average were about 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18 °C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, the difference appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence later growth as earlier reported from studies of Atlantic salmon Salmo salar. This article is protected by copyright. All rights reserved.