Fathead minnows use chemical cues to discriminate natural shoalmates from unfamiliar conspecifics.

Naturally occurring shoals of fathead minnows (Pimephales promelas) were captured and individuals given the choice between shoalmates and unfamiliar conspecifics in a two-choice discrimination test. When presented with chemosensory cues alone or with both chemosensory and visual cues, minnows exhibited a significant preference for shoalmates versus unfamiliar conspecifics. With visual cues alone, there was no significant discrimination of shoalmates. A second set of trials was conducted to ensure that minnows were choosing natural shoalmates and not just individuals with which they were held in the laboratory. When given the choice between unfamiliar conspecifics and shoalmates from which they were separated for a minimum of two months, minnows exhibited a significant preference for shoalmates. Taken together, these data suggest that fathead minnows are able to discriminate among conspecifics on the basis of familiarity using chemosensory cues, even after a relatively long separation. The ability to discriminate among conspecifics may facilitate: (1) the maintenance of kin groups or groups that share similar foraging or predator avoidance patterns or (2) the recognition of former shoalmates after some period of separation.