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Catostomidae (suckers; subclass Actinopterygii, order Cypriniformes) A fairly large family of freshwater fish: they resemble minnows, but have a protrusible sucker-mouth which is used to ingest organic material from the river bottom. Many have large scales, a single dorsal fin, and a body that is round in cross-section. Schools of mature suckers are known to undertake spawning migrations upstream in the river. Although most of the 58 species live on the N. American continent, two species are found in eastern Siberia and China.