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We used laboratory and field-based experiments to examine male mate choice in the promiscuous Panamanian bishop Brachyrhaphis episcopi (Poeciliidae) (also referred to as Brachyraphis episcopi). As females of this species can store sperm, males could increase their reproductive success by selectively mating with different females. To test this, males in both the laboratory and field were allowed to choose between a familiar (same tank or pool) and an unfamiliar female (different tank or pool). We compared males from streams and seasonally occurring pools to see whether lack of access to new females in pools promotes male mate choice for unfamiliarity. In addition, we chose streams and pools both with and without predatory fish to examine the influence of predation risk. In both the laboratory and the field, males attempted more matings with unfamiliar than familiar females. Field experiments showed that courtship preferences differed between males from populations with and without predatory fish: males from populations with predators were choosy only when light levels were dim, whereas males from populations without predators were choosy when light levels were brighter. Males from both streams and pools discriminated between familiar and unfamiliar females, but there were no differences in mating preferences between males from each habitat. Although the reasons for a preference for unfamiliar females remain unclear, the plasticity of this behaviour is evident. Differences in male mate choice between populations with and without predators suggest that males may face a trade-off between the costs and benefits of being choosy. [Copyright &y& Elsevier]