Growth and sexual maturation of six stocks of brown trout Salmo trutta L. in culture

The growth dynamics of six different Swedish stocks (Arjeplog, Arevattnet, Bergnäs, Båthälla, Granbo. Gullspång) of landlocked brown trout were compared. The fish were kept in 1-m² troughs from start of feeding in spring 1988 until September 1989. Thereafter the stocks were reared together in 4-m² troughs until the termination of the experiment in October 1990. After the first summer of growth, Bergnäs trout had the highest mean weight and Granbo and Båthälla trout the lowest. In September 1989 the ranking of stocks with respect to mean weight had not changed. During the rest of the experiment, i.e. when stocks were reared together, Arevattnet trout increased in weight most rapidly and reached the highest final mean weight. Bergnäs trout grew very slowly after the stocks had been merged. Granbo and Båthälla trout ended up with the lowest mean weights. Sexual maturation in 1 + males was very rare. Gullspång trout had the highest proportion (42%) of mature 2+ males, while Granbo trout had the lowest proportion (4%). With the exception of Gullspång trout, mature males generally had a higher mean weight than immature fish. The experiment revealed considerable differences in overall growth, even between stocks with similar life histories in nature. Hatching time, frequency of sexual maturation and hatchery selection were identified as potential mechanisms behind the observed differences. In all, stock differences in important traits for commercial aquaculture are considerable, which makes further stock comparisons necessary before the start of breeding programmes.