Abstract
The poor results of lake-migratory brown trout, Salmo trutta lacustris L., restoration in Lake Hańcza Nature Reserve prompted undertaking the current study that sought to verify if hatchery-reared fish age 2+ can survive the critical period of acclimation and remain in the lake. Thirty-one individuals were tagged with coded acoustic transmitters and observed for 317 days. This method helped to analyze: 1) the spatial behavior of tagged fish for one year following their release; 2) the possible differences in the behavior of fish released in various places habitually used for stocking. By the end of study, 6.5–12.9% of the tagged fish remained in the lake. The most interesting phenomenon the data indicated was the trout behavior in late spring and early summer, when the fish moved vigorously along the longitudinal axis of the lake continuously for several weeks. The reasons for the fish movements observed in Lake Hańcza were not clear. For this unique species/population it is important to determine whether such behavior is typical of this fish also in other water bodies and if it is only seen in hatchery-reared fish aged 2+ and 3+.