Richardsonius is a genus of freshwater ray-finned fishes belonging to the family Leuciscidae, the shiners, daces and minnows. The fishes in this genus are found in western North America. Commonly known as redside shiners, that term is also used to refer to Richardsonius balteatus specifically. The genus is named after naturalist Sir John Richardson (1787–1865), who described R. balteatus in 1836.

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