Behaviour of mature anadromous char (Salmo alpinus L.) towards odorants produced by smolts of their own population.

Mature anadromous char (Salmo alpinus L.) of a specific population were tested in behaviour experiments with respect to attraction effects of smolts of the same population, smolt material, and chemical fractions of that material. The char reaction indicated preference for intestinal contents and possibly bile from own population over skin mucus material and food. Chemical fractions isolated from the intestinal contents were tested for attraction at a concentration of 1.5 x 10(-9) g per 1. One of the fractions attracted the mature char. The results are discussed in relation to the "migration pheromone" hypothesis proposed by Nordeng (1971) as being crucial for the return of anadromous salmonids to their home river's spawning grounds.