9 



Origin and Affinities of the Freshwater 

 Fish Fauna of Western North America 



Robert Rush Miller 



Museum of Zoology, University of Michigan, 

 Ann Arbor 



1 he area covered by this paper is primarily 

 North America west of the Continental Divide, northward to 

 the Stikine River, British Columbia, and southward to the Rio 

 Yaqui, northwestern Mexico. The Yaqui is included because it 

 contains certain faunal elements derived from the Colorado River, 

 and British Columbia is treated since its coastal streams include a 

 number of Columbia River types (Lindsey, 1957). Excluded from 

 consideration, except in passing, are the Arctic and Bering Sea 

 drainages, and only mentioned is the interdigitation of Nearctic 

 and Neotropical fishes in Middle America. 



Thirty families comprising nearly 200 species have been recorded 

 from fresh water within this area (Table I). These groups form a 

 diverse assemblage. Twelve of the families include species in the 

 Western fauna that are predominantly marine, although some 

 inhabit brackish water or invade fresh water to a limited extent, 

 especially toward the tropics, e.g., herrings, flatfishes, silversides, 

 mullets, sticklebacks, and gobies. Representatives of four families 

 regularly pass only part of their life cycle in the sea or in fresh water 

 (lampreys, sturgeons, some smelts, and most trouts). Species repre- 

 senting four families were derived from marine ancestors but they 

 are now virtually restricted to fresh water (a gizzard shad, Dorosoma ; 

 a codfish, Lota; a viviparous perch, Ilysterocarpus ; and the fresh- 

 water sculpins, Cottus). Two families, the whitefishes (Coregonidae) 

 and graylings (Thymallidae) , are intimately related to the salmons 

 and trouts (Salmonidae), which occur in either the sea or fresh water. 



In interpreting origins and dispersal patterns it is essential to 

 distinguish the true freshwater fishes from these groups. Although I 



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