Barriers to Dispersion of River Fishes 299 



water communication, has no appreciable importance, is shown 

 by the almost absolute identity of the fish faun;e of Lake Winne- 

 bago and Lake Champlain. While many large fishes range 

 freely up and down the Mississippi, a majority of the species 

 do not do so, and the fauna of the upper Mississippi has more 

 in common with that of the tributaries of Lake Michigan tlian 

 it has with that oi the Red River or the Arkansas. The m- 

 fluence of chmate is again shown in the paucity of the fauna 

 of the cold waters of Lake Superi(-)r, as compared with that 

 of Lake Michigan. The maj(_-irity ni our species cannot endure 

 the cold. In general, therefore, cold or Northern waters con- 

 tain fewer species than Southern waters do, though the num- 

 ber of individuals of any one kuid mav be greater. This is 

 shown in all waters, fresh or salt. The fislieries of the Northern 

 seas are more extensiA'c than those of the tropics. There are 

 more fishes there, but they are far less A'aried in kind. The 

 writer once caught seventy-five species of fishes in a single 



Fig. 190. — Peristedion minialum Goode and Bean, a deep-red colored ILsh of 

 the depths of the Gulf Stream. 



haul of the seine at Key West, while on Cape Cod he obtained 

 with the same net but forty-five species in the course of a week's 

 work. Thus it comes that the angler, contented with many 

 fishes of few kinds, goes to Northern streams to fish, while the 

 naturalist goes to the South. 



But in most streams the difference in latitude is insignificant, 

 and the chief differences in temperature come from differences 

 in elevation, or from the distance of the waters from the colder 

 source. Often the lowland waters are so difi^erent in character 

 as to produce a marked change in the quality of their fauna. 

 These lowland waters may form a barrier to the free movements 



