The caudal fin is weak and slightly forked. Above the black stripe are numerous reddish-bronze scales with dark spots. Below the stripe the body is silvery and the ventral surface is white. The upper head surface is black, the lower is white. The fins are slate blue.
Females have an entirely black upper surface, occasionally tinged with a reddish coppery hue.
Cui-ui usually breed upstream in the Truckee river or, when a school cannot make it upstream, they spawn in inflowing freshwater at the mouth of the river. Spawning occurs in relatively shallow, rapidly flowing water, often at the head of a sand or gravel bank which turns or parts the current. Two or more males attend a single female. Eggs are small and abundant, the habit of depositing eggs in shallower water being extremely tiring due the sudden fall in water depth. Cui-ui are omniverous, essentially zooplankton feeders.