Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan
Magnetosensitivity of the darkbanded rockfish Sebastes inermis was examined by conditioning and electrocardiography. It had earlier been demonstrated that the transported and released fish do not home properly when they have a magnet bar inserted in the stomach. The fish were conditioned to an imposed magnetic field of 192,473 nT parallel or vertical to the fish body placed along the earth's west-east axis. After 10-20 conditioning runs, the fish exhibited a significant conditioned response (i.e., slowing of the heart beat) to a 192,473 nT magnetic field and even to a 2,533 nT magnetic field that combined with the geomagnetic field (horizontal component 31,690 nT, vertical component 32,816 nT) at our laboratory to produce a resultant magnetic field of 5° horizontally or 44° vertically. These results indicate that the fish have high magnetosensitivity. It is suggested that the fish can find their home using a geomagnetic sense.