The cui-ui Chasmistes cujus, a long-lived (40 years or more) and highly fecund catostomid, is often prevented from spawning in drought years. We studied the effect of cui-ui age on egg viability and the effect of nonannual spawning on fecundity in relation to length, age, and growth rate. Egg hatching and survival of swim-up larvae were examined for the offspring of first-time spawners, intermediate-aged females, and old females. Fecundity was tested for three growth categories (fast, intermediate, and slow) in years that were sufficiently wet to allow fish to spawn in the Truckee River and after dry years when fish did not spawn because of river inaccessibility. Females in the fast-growth category were first-time spawners, those in the middle-growth category were young to middle aged, and those in the slow-growth category were middle aged to old. Females up to 44 years of age still had viable eggs and a reproductive life of at least 29 years. Fecundity was greater after no-spawn years (dry year) compared with a spawn year (wet year), especially for fish in the slow-growth category. This study provides insight into the reproductive adaptation of a long-lived western North American catostomid and suggests possible reasons for the wide variation in fecundity in other long-lived catostomids. Our data will be used to improve the accuracy of an existing cui-ui population viability model. The revised model will have greater sensitivity to cui-ui survival relative to their spawning frequency and, thus, contribute to better management of conditions needed for the long-term survival of endangered cui-ui.