Previous research has indicated that lake-migrating sockeye salmon fry have compass directional preferences, cued in part by magnetic fields. This paper reports the results of experiments designed to compare the magnetosensory system of salmon with those of other organisms. Unlike birds, the fry did not reverse their compass orientation 180° when the magnetic field's vertical component was inverted, but rather displayed northerly (31°) orientation similar to that of fry in two different control conditions (325° and 22°). These results agreed with the 349° bearing displayed in 1979.
Magnetized material (implicated as possible transducers in the magnetosensory systems of bacteria, honeybees, and homing pigeons) was not found (<2 × 10−7 e.m.u.) in 26 out of 30 fry examined. The material in the other 4 was probably environmental contamination, and not part of a sensory system. The mechanism of magnetic detection in salmon remains unknown, but consideration of the evolution and life history of the fish provides some clues as to the possible nature of the mechanism.