Influence of weak electric and magnetic fields on turning behavior in elvers of the American eel Anguilla rostrata

The turning behavior of elvers of the American eel Anguilla rostrata was studied in an arena in which a horizontal electric or a vertical magnetic field could be manipulated. The objectives were to determine if the strength and polarity of a weak direct-current (dc) electric field influenced elver orientation, and to determine if any such influence was due to electric fields generated by the elvers' own swimming movements. As electric current density increased from 10^-2 A cm^-2 to 10² A cm^-2, elvers turned increasingly more toward the anode, regardless of whether the anode was on the left or right side of the arena. Elvers in the lowest field turned more toward the cathode than control elvers, and elvers in the highest field turned more toward the anode than controls. There were no differences in mean turning angles of groups of elvers swimming in four different vertical magnetic field conditions (0.54 gauss, <0.02 gauss, 0.52 gauss reversed direction, and 2.00 gauss), suggesting that elvers were not influenced by internally generated electric fields. However, swimming speeds were such that the generated fields would have been of the order of 10^-4 A cm^-2 or less. Elver orientation apparently could be influenced by electric fields of the magnitude generated in major ocean current systems, but probably are not influenced by electric fields generated by their own swimming in the geomagnetic field.