Fig. 6.
Alarm substance treatment significantly reduced the distance among zebrafish irrespective of the presence or absence of the predator. 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) with predator present = 10; control (zero alarm substance) with predator absent = 10; high concentration alarm substance with predator present = 10; high concentration alarm substance with predator absent = 10. 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 with time, the difference between the alarm substance treated and the control groups increased: the former showed decreased distance among shoal mates and the latter did not. Also note that despite that the experimental zebrafish had full access to cues of all modalities about the predator, the presence or absence of the predator had no significant effect. For procedural details, see Section 2. For details of the results of the statistical analysis, see Section 2.