Distribution of fish between two compartments in Experiment 1. A, B: trials where lake water with parasites was added to one of the end compartments. C, D: control trials where lake water without parasites was added to both end compartments. A, C – tests on solitary fish; B, D – tests on fish in groups of 5. NFR, ind – index of fish number in different compartments as a sum of 3 consecutive counts of fish for each 15 min. NFR values for the groups of 5 fish were divided by 5. Black circles: NFR for the parasitized compartment, or for a randomly chosen compartment in the control trials. Open circles: NFR for the opposite compartment. Means and SE bars are shown.