The American paddlefish (Polyodon spathula) are long-lived, and sexually late maturing. Females do not begin spawning until they are seven to ten years old, some even as late as sixteen to eighteen years old. Males begin spawning around age seven, some as late as nine or ten years of age. American paddlefish spawn in late spring provided the proper combination of events occur, including water flow, temperature, photoperiod, and availability of gravel substrates suitable for spawning. If all the conditions are not met, America paddlefish will not spawn. Research suggests females do not spawn every year, rather they spawn every second or third year while males spawn more frequently, typically every year or every other year.