Abundance and growth data indicated a 2-yr life cycle for longfin smelt with even-numbered year-classes being more abundant and showing a lower growth rate than the odd. The Cedar River was the major spawning area. The peak of the spawning run occurred during mid-March in 1970 and mid-February in 1971. The average size of spawning adults decreased as the spawning runs progressed. Males were consistently larger than females and dominated in numbers throughout the runs by a 3:2 ratio. The time of the spawning migration was related to body size; the larger adults of the odd year-class spawn earlier in the year than the smaller adults of the even year-class.