The Lahontan redside Richardsonius egregius is a cyprinid fish of the Great Basin in eastern California and western Nevada.

Lahontan redsides are noted for their breeding colors, consisting of a bright red stripe with a yellow border on each side. At other times, the stripe is still visible, but the red is much reduced, leaving a gradual transition from the olive-colored back to silvery underside. Overall shape is slender, with a large eye and terminal mouth. The dorsal fin has 7-8 rays, while the anal fin has 8-10 rays. The pectoral fins are somewhat long, the tips reaching nearly to the bases of the pelvic fins. The tail is deeply forked. Total length ranges up to 17 cm, but an 8 cm length is more typical of mature adults.