CONDITIONS OF LIFE 297 



sea for the same purpose. The former are called anadromous 

 and the latter katadromous. The most important anadromous 

 fishes are species of Salmo in the North Atlantic and Oncho- 

 rhynchus in the North Pacific. The salmon, Salmo sa/ar, may- 

 enter rivers at almost any time in the summer but there is 

 usually a more definite migration in autumn, and the fish travel 

 up stream to the highest parts of the rivers, jumping through 

 rapids and falls which are not too high, till they reach the 

 gravelly beds in which they make their redds, that is to say in 

 which the female scoops out furrows for the reception of the 

 eggs and heaps gravel over them. The fish take little or no 

 food during this migration and the males fight fiercely 

 together ; their condition therefore deteriorates greatly and 

 when the spawning is over they are exhausted and emaciated, 

 with discoloured and usually abraded skins. In this condition 

 many die of exhaustion or fall victims to disease, in which they 

 are attacked by the salmon fungus, Saprolegnia ferax. A 

 certain proportion, however, return to the sea, recover their 

 health and vigour and spawn repeatedly. The following account 

 is given of the king salmon or quinnat of the Pacific coast of 

 North America by American ichthyologists : This great fish, 

 Oncorhynchus yschawitscha, spawns in November at the age of 

 four years and the average weight of 22 lbs. In the Columbia 

 river it begins running with the freshets in March and April ; 

 it spends the whole summer without feeding in the ascent of the 

 river. By autumn the fish have reached the mountain streams 

 of Idaho, greatly changed in appearance, discoloured, worn, and 

 distorted. The males are hump-backed, with sunken scales and 

 greatly enlarged, hooked, bent, or twisted jaws, and enlarged 

 dog-like teeth. On reaching the spawning grounds, which may 

 be 1 OCX) miles from the sea in the Columbia, over 2000 in the 

 Yukon, the female deposits her eggs in the gravel of some 

 shallow brook ; the male covers them and scrapes the gravel 

 over them. Then both male and female drift, tail foremost, 

 helplessly down the stream ; none, so far as certainly known, 

 ever survive the reproductive act. The same habits occur in five 

 other species of Oncorhynchus in the North Pacific, but in these 

 the fish do not start so early nor run so far. The size and 

 weight of the quinnat ascending rivers varies enormously, some 

 of the males being only eight inches long, but the smallest 



