The importance of learning for sibling odor preference in juvenile Arctic char was analyzed in the present study. Fish were reared in the following eight conditions: (1) communally with siblings for 15 months; (2) communally with siblings for 17 months; (3) in isolation since fertilization; (4) in isolation since fertilization and exposed to sibling scent during the whole rearing period; (5) in isolation since fertilization and exposed to sibling scent from time of free swimming; (6) in isolation since fertilization and exposed to sibling scent during the whole rearing period, except two months without scent until testing; (7) in isolation since fertilization and exposed to sibling scent from time of free swimming, except two months without scent until testing; and (8) communally with siblings followed by a two-month isolation until testing. Char were followed individually in a Y-maze (fluviarium test) with a video-computer-based image analysis system for 12 hr. Sibling-scented water was supplied to one lateral half of the test area and water from non-siblings on the opposite half. Isolated individuals without any preexposure to siblings showed no significant preference. Test fish reared with siblings and those that had been reared in isolation but exposed to sibling scent until testing preferred water conditioned by their own siblings. Isolated fish that had been exposed to sibling scent since fertilization, or since free swimming, followed by a two-month period with only pure water, showed no significant preference. Char isolated for two months after being communally reared preferred water scented by siblings. The results demonstrated that behavioral discrimination between siblings and nonsibling odors occurred after total isolation (isolated both from siblings and sibling odors) only in individuals that had been communally reared. This may suggest that social interactions are important for learning and long-term memory of sibling odors in Arctic char.