In many social fish species, visual cues play an important role in inducing shoaling behavior. The research group of Associate Professor Eiji Watanabe and researcher Tomohiro Nakayasu, of the Laboratory of Neurophysiology at NIBB, has examined whether and how “biological motion” depicting a moving creature by means of only a small number of isolated points induces shoaling behavior in fish for the first time. Medaka (Oryzias latipes) were used because they are known to have high visual acuity and exhibit a strong tendency to form shoals. In experiment 1, the group found that the presentation of medaka biological motion resulted in heightened shoaling behavior when compared with that of non-biological motion (depicted by a small number of points placed at fixed distances that moved at a constant speed in a constant direction). In experiment 2, it was indicated that medaka biological motion was more effective at inducing shoaling behavior when compared with human biological motion. In experiment 3, it was demonstrated that shoaling behavior was largely dependent on the smoothness of the biological motion. In experiment 4, it was revealed that shoaling behavior was maximized in normal speed group and decreased in faster- and slower-than-normal speed groups. In experiment 5, it was shown that shoaling behavior was slightly reduced when a reversed movie was presented. These results suggest that motion information extracted from conspecifics was sufficient to induce shoaling behavior in medaka and that deviation from normal and familiar motion impeded shoaling behavior. The naturalness of motion may be responsible for the induction of shoaling behaviour.
Dr. Tomohiro Nakayasu and Associate Professor Eiji Watanabe