Learned magnetic field discrimination in yellowfin tuna,Thunnus albacares

Summary1.Yellowfin tuna,Thunnus albacares, were trained individually to discriminate between two Earth-strength magnetic fields by differential reinforcement of a swimming response.2.Seven subjects, of which two were trained with a double blind procedure designed to control for the possibility of cues from the experimenter, learned to discriminate between ambient and altered fields (Figs. 1–3).3.Two additional fish trained with the same double blind procedure failed to discriminate between two magnetic fields in which the gradients of intensity were equal and opposite (Fig. 4).4.The results suggest that the responses to magnetic fields by yellowfin tuna are neurally mediated and that magnetic field detection by this species can be analyzed by the same means as other sensory modalities.