1036 FRESH-WATER BIOLOGY 



others, with both range and home in fresh water, belong to present 

 marine families and have evidently comparatively recently become 

 members of the fresh-water fauna. 



A notable example of a fish comparatively recently contributed 

 by the sea to fresh water is Ilysterocarpus traski Gibbons. It is a 

 viviparous fish of the rivers of central California. All of its rela- 

 tives live in the Pacific Ocean from which it is an undoubted 

 immigrant. 



The sea basses furnish several illustrative examples. The striped 

 bass, Rocciis lineatus, is an oceanic fish entering rivers to spawn, 

 while its nearest relative, Roccus chrysops, the white bass, is con- 

 fined to the Great Lakes and upper Mississippi Valley. Closely 

 related to these are the yellow bass, Morone interrupta, of the lower 

 Mississippi Valley, and the white perch, Morone americana, in 

 salt and fresh water from Nova Scotia to South CaroHna. The 

 ninety other American members of this family are all marine. 



Various species of Robalos (Centropomus) enter fresh water. 



The Mugilidae have added various species to the fresh waters 

 south of the United States. The Atherinidae have contributed the 

 skipjack to our rivers and lakes, and south of us this marine family, 

 whose eggs are provided with threads, has contributed and is con- 

 tributing to the fresh waters all the way from Mexico to Patagonia. 



Fig. 1538. Skipjack, Labidcstcs skulus (Cope). Actual size, 95 mm. long. 



The sticklebacks and killifishes help to bridge the gap, if such 

 exists, between the fresh waters and the ocean. Even the pipe- 

 fishes and flounders have a tendency to colonize fresh waters, and 

 the flounders at least have succeeded in South America. 



The Sciaenidae, a marine family, has contributed the thunder- 

 pumper or white perch to the Great Lakes and Mississippi Valley, 

 and several other species to the streams of South America. Some 

 of its marine species occasionally run up streams. 



The large family of the Cottidae has added the miller's-thumb. 



