Morphology, time of formation and deposition of the first increment, and rate of increment deposition were determined for sagittae, lapilli, and asterisci from Lost River suckerDeltistes luxatusand shortnose suckerChasmistes brevirostris. Sagittae and lapilli form on the day of hatch, and asterisci form after 41–52 d in Lost River sucker and after 14–25 d in shortnose sucker. Lapillus increments were validated by using known-age hatchery-raised larvae and wild-caught larvae and juveniles marked by immersion in water with an alizarin complexone concentration of 50 mg/L for 4 h and 18 h, respectively. A transition from relatively wide to relatively narrow increments was sometimes seen during the second week after hatch and appears to be associated with yolk absorption. Because of their readability and conservative growth, lapilli are the preferred otolith structure for age determination of larval and juvenile suckers, whereas sagittae are preferred for nonostariophysan fishes.