Cave fishes need to rely on non-visual senses,
such as the sense of smell or the lateral line to communicate in darkness. In the present study, we investigated sex identification by females of a cave-dwelling livebearing fish, Poecilia mexicana (cave molly), as well as its surfacedwelling
relatives. Unlike many other cave fishes, cave
mollies still possess functional eyes. Three different modes of presentation of the stimulus fish (a male and an equally sized female) were used: (i) the stimulus fish were presented behind wire-mesh in light, allowing the focal female to perceive multiple cues, (ii) the experiment was
carried out under infrared conditions, such that only nonvisual cues could be perceived and (iii) the stimulus fish were presented in light behind transparent Plexiglas, allowing for the use of visual cues only. Females of all populations examined preferred to associate with the stimulus female in at least one of the treatments, but only
when visible light was provided, suggesting that far-range sex recognition is limited or even absent in the cave molly under naturally dark conditions.