BRANCH CHORD AT A; CLASS PISCES: THE FISHES 289 



herring, and mackerel caught. ' ' Among our fresh-water 

 fisheries the great salmon fisheries of the Penobscot and 

 Columbia rivers and of the Karluk and other rivers of 

 Alaska are the best known. The whitefish of our Great 

 Lakes is also one of the important food-fishes of the world. 



In many places fishes are raised in so-called hatcheries, 

 not usually for immediate consumption but for the purpose 

 of stocking ponds and streams either in the neighborhood 

 of the hatchery or in distant waters which the special 

 species cultivated has not been able naturally to reach. 

 The eggs of some fishes are large and non-adherent, two 

 features which greatly favor artificial impregnation and 

 hatching. In the hatcheries the eggs are put first into 

 warm water, where development begins; they are then 

 removed into cool water, which arrests development with 

 out injury, making shipment possible. The eggs of 

 salmon and trout in particular can be sent long distances 

 to suitable streams or ponds. The eggs of the shad have 

 been thus carried from the East to the streams of Cali- 

 fornia and trout have been distributed to many streams in 

 our country which by themselves they could never have 

 reached. 



The salmon is a conspicuous example of those fishes 

 which can be artificially propagated. The eggs of the 

 salmon are large, firm, and separate from each other. If 

 the female fish be caught when the eggs are ripe and 

 her body be pressed over a pan of water the eggs will 

 flow out into the water. By a similar process the milt or 

 male sperm-cells can be procured and poured over the 

 eggs to fertilize them. The young after hatching are kept 

 for a few days or weeks in artificial pools, till the yolk- 

 sacs are absorbed and they can take care of themselves. 

 They are then turned into the stream, where they drift tail 

 foremost with the current and pass downward to the sea. 

 All trout may be treated in similar fashion, but there are 



