208 



R. R. MILLER 



Colorado River Complex 



The primary fish fauna of this basin, including that of the late 

 Pleistocene tributary White River of eastern Nevada (Hubbs and 

 Miller, 1948, pp. 95-98), is the richest and has the highest per- 

 centage of species endemism (87 per cent) of the seven major drain- 

 ages. Two factors contribute to this: (1) the basin developed as 

 isolated segments for a long period prior to its formation as the 

 continuous river we see today ; and (2) it has fewer competing groups 

 of marine derivation than the three other coastal drainages (Sacra- 

 mento, Klamath, and Columbia) and about half of these {Elops, 

 Mugil, Eleotris, Gillichthys) are restricted to the terminal portion of 

 the river and the others (Prosopmm, Salmo, Cottus) mostly to the 

 higher headwaters. 



The affinities of the fishes vary in different parts of the Colorado. 

 Cutthroat trout {Salmo clarki), mountain whitefish (Prosopmm 

 williamsoni, Fig. 17) and sculpins {Cottus bairdi and C. annae), all 

 confined to the upper portion, have their closest relatives in the 



Fig. 17. Breeding male and juvenile of the mountain whitefish, 

 Prosopium williamsoni, a species of cold, clear mountain streams that has 

 probably dispersed by stream capture. (From Jordan and Evermann, 

 1900, Figs. 200, 200a.) 



