HOMING BEHAVIOR OF DISPLACED STREAM-DWELLING BROWN TROUT

Aspects of resident behaviour in native brown trout, Salmo trutta, were studied in two experiments. In the first experiment, 50% of trout caught by electrofishing were made anosmic by removal of the olfactory rosettes, and then all fish were displaced 200 m either up or downstream. Very few fish lacking the olfactory organ returned to their home area within 9 weeks, but more than 40% of the sham-operated control fish from both the up and downstream displacement groups returned. Sexually maturing and immature fish returned at the same rate. In the second experiment, some fish from a small tributary brook were released in the main stream, 150 m above the junction with the tributary. Twenty-four per cent returned to their tributary within 9 weeks, demonstrating an ability among the fish to combine negative and positive rheotaxis in homing behaviour. This work shows that stream-dwelling brown trout can return home when displaced outside their normal range, and that olfaction is important for this behaviour. © 1990 The Association for the Study of Animal Behaviour.