318 ANIMALS IN INLAND WATERS 



mass of fish going up is so enormous that, instead of nets being used 

 to catch them, large bucket-wheels are employed to scoop them out. 

 One such wheel can catch as many as 14,000 fish in one day. 25 The 

 immense numbers of the whitefish Coregonus leucichthys and other 

 species which come up the Obi and the Irtysch in the spring furnish 

 opportunity for great draughts of fishes by the inhabitants of these 

 regions. In the relatively short rivers of east Siberia which flow to the 

 Pacific from the Okhotsk highlands, the keta (Oncorhynchus keta) 

 comes up in such great numbers to the brooks at their sources that 

 the streams are not large enough to hold the fish ; their backs protrude 

 out of the water, they are crowded against the banks; some perish, 

 while masses of others become the prey of birds, bears, dogs, and 

 people. It is unlikely that any of these migrants ever return to the 

 ocean; even those which finally spawn perish in the end from sheer 

 exhaustion. 26 



An interesting and unexpected result of American fish tagging ex- 

 periments, particularly on the Pacific coast, is found in the evidence 

 that salmon and fishes of similar habit have a strong tendency to 

 return to the brook in which they were spawned, when they in turn 

 are sexually mature. The mechanics of this process whereby the fishes 

 are able to detect significant differences to guide them in their return 

 migration have not yet been discovered. These studies have also 

 shown that fishes living in a long stream are physiologically different 

 from those of the same species from a shorter river. 



In the rivers of the far north such migratory fishes make up an 

 important part of the fauna, for many salmon remain permanently 

 in the streams. There are only two species of salmonids in the rivers of 

 northern Siberia which are entirely independent of the ocean, the 

 grayling Thymallus thymallus, and a trout, Salmo coregonoides; be- 

 sides these, seven other species inhabit these waters. It is probably this 

 migratory habit which enables the Salmonidae, of all fresh-water 

 fishes, to penetrate farthest to the north. Chars {Salmo arcturus and 

 S. naresi) have been caught even as far north as Grinnell Land, 82° 

 34' N. latitude. The migration of fish from the seas to rivers is paral- 

 leled in other situations by the migration of fish from large to small 

 streams as red horse and suckers do in the Mississippi valley. 



BIBLIOGRAPHY 



1) Skorikow, 1902, Biol. Zbl., 22, p. 551-570.— 2) Woltereck, 1908, Int. Rev. 

 Hydrob., 1, p. 303.— 3) Galtsoff, 1924, Bull. Bur. Fisheries, 39.-4) Welch, 1935, 

 Limnology. — 5) Needham & Lloyd, 1916, Life of Inland Waters. — 6) Stein- 

 mann, 1915, Praktikum der Siisswasserbiologie, 1, p. 17. — 7) Smolian, 1920, 



