Orientation responses of American eels, Anguilla rostrata, to varying magnetic fields.

1. The locations of freshwater yellow eels in an eight-chambered octagonal behavior tank were videotaped during six-day intervals while the animals were being subjected to normal and experimental magnetic fields. 2. The earth's magnetic field (0.5 g) was utilized for two control periods at the start and completion of each run for each animal. 3. During each run, the sequence of applied magnetic fields was +1.0, 0.0, -0.5 and -1.0 g, each being applied for a period of 24 hr. 4. Under the influence of the earth's magnetic field, the eels showed a preference for a northeast direction (27.01%). During the second control period (i.e. after being subjected to variations in the magnetic field), the animals showed a dual preference for north and northwest directions (23.02% and 25.9%, respectively). 5. In a 0.0 g field, the eels preferred the north chamber (24.43%) and the vestibule of the behavior tank (19.46%); a preference for north was also obtained with a field of +1.0 g (25.95%). 6. The preferred direction with the -0.5 and -1.0 g fields was southeast (20.93 and 26.71%, respectively).