A small member of the minnow family with an elongated body that is flattened ventrally. There are eight rays in the dorsal fin and seven in the anal fin. The lateral line has approximately 65 scales. Coloration tends to be olivaceous background, with a lot of blotches in darker pigments. There are whitish spots at the origin and insertion of the dorsal fin and dorsal and ventral portions of the caudal fin base. A black, basicaudal spot is usually present. Breeding males have bright red-orange coloration at the bases of the paired fins and on the adjacent body, on the base of the caudal lobe, about the mouth, near the upper portion of the gill opening, and often on the abdomen. Females in the breeding season become yellowish on the fins and lower body.

Loach minnow was originally classified as Rhinichthys cobitis by Charles Girard in 1856. However, its taxonomic status was revised in 2017 (Smith et al.) to Tiaroga cobitis to better reflect our current understanding of the fish’s evolutionary development from more recent morphological and genetic data.