Rhetotaxis in Zebrafish: Is Magnetotaxis Involved?

Fish orientation is a complex issue requiring the integration of different cues, including water currents and geomagnetism. Zebrafish (Danio rerio) show positive rheotaxis and there is evidence that they also respond to geomagnetic fields. We investigated how the magnetic field, in the range of geomagnetic intensities (±50µT), affect the rheotactic response of zebrafish. We conducted experiments by a swimming tunnel wrapped with a solenoid on three experimental groups: shoal, individuals and Co²⁺ treated shoal . Cobalt treatment allowed testing the involvement of lateral line in this response. We observed that, in absence of water current, the animals show an upstream preference in the orientation only when they have had a previous experience of the flow in the tunnel and in presence of magnetic field. Furthermore, we found that the direction and intensity of magnetic field affect the relationship of both upstream swimming time and schooling time with water flow speed. Lateral line and interaction among individuals play an important role in this rheotactic-magnetic response. We conclude that magnetic field is involved in the framework of cues that participate to rheotaxis.