Fig. 2.
Alarm substance treatment significantly reduced the distance among zebrafish. Mean + S.E.M. is shown. Sample sizes (n) represent the number of five-fish shoals tested and are as follows: control (zero alarm substance) = 13; low concentration = 15; medium concentration = 13; high concentration = 15. The distance among shoal mates is calculated as the average of distances, expressed in cm, between all possible pairs of zebrafish of the shoal. Note that while zebrafish in the highest concentration group reduced the distance (increased their shoal cohesion) with time, the control fish (zero alarm substance) did not. Also note that throughout the session zebrafish could view a fish predator swimming in a stimulus tank adjacent to the observation tank. For procedural details, see Section 2. For details of the results of the statistical analysis, see Section 3.