SENSORY MECHANISMS OF HOMING IN SALMONID FISH .I. INTRODUCTORY EXPERIMENTS ON OLFACTORY SENSE IN GRILSE OF BALTIC SALMON (SALMO-SALAR)

'Grilse' of Baltic salmon are young sexually mature fish, mostly males. In 191 'grilse' of River Indalsälven the olfactory sense was eliminated and then the fish were released in the Sundsvall Bay Area 35-40 km north and south of the home river. Most of these fishes failed to orient toward home during spawning time, whereas many of the 100 control animals traumatized on the nose homed as readily as did many of the 100 untreated controls released in the same places. These results indicate an important role for olfaction in homing behaviour and migration in Baltic salmon.