Conservation of stream fishes requires an understanding of how their reproduction and recruitment are affected by environmental conditions. Flow regulation and habitat loss in North American Great Plains streams threaten many native fishes, including pelagic-broadcast spawning cyprinids. Pelagic-broadcast spawning by flathead chub (Platygobio gracilis), a species declining throughout much of its extensive range, began after temperatures exceeded 15 °C in Fountain Creek, Colorado (USA), despite different annual flows. Alternatively, streamflow patterns controlled recruitment of juveniles because high-magnitude summer flows (spikes) reduced abundance of larvae hatched just prior to or during such events. Juvenile recruitment was highest for larvae hatched just after summer flow spikes occurred or during stable base flow periods. Understanding environmental conditions suitable for reproduction as well as subsequent recruitment should inform conservation actions, especially in flow-altered streams, and improve prospects for persistence of imperiled Great Plains cyprinids, including flathead chub.
