Other Salmonidw. 189 



active fish, ready to start out on a new career in a larger 

 field of activity. He begins life well equipped with a 

 stock of provisions stored up in a knapsack which he 

 carries upon his belly. This sac contains a portion of 

 the food on which he lives for the next fortnight or 

 more of his life, but being small as compared with the 

 bulk of his body, it is no impediment to active and 

 vigorous movement. He belongs to what is termed the 

 "buoyant" fishes, swimming freely at all times from 

 his birth, in this respect differing from the trout with 

 its enormous sac, which encumbers its movements so 

 that it lies for days prone upon its side almost helpless. 

 This marked difference between the whitefish and trout 

 makes it possible to hatch whitefish by the hundred 

 millions, while the hatching of trout is limited to a few 

 millions, and at a greatly increased cost. The white- 

 fish can be hatched in automatic jars, because when the 

 young fish hatches he comes to the top of the jar and 

 goes over with the outflow of water, while the trout, 

 weighted down with his heavy sac, falls to the bottom 

 of the jar. The specific gravity of trout eggs is greater 

 than that of the whitefish, and the force of water re- 

 quired to keep them in motion wears the sac of the 

 trout and results in premature hatching. 



Observations made on whitefish fry at the Detroit 

 hatchery for two or three years has settled beyond 

 question the fact that the young fish begins to take 

 food, by the mouth, sometimes as early as the third day 

 after hatching, and within four or five days quite free- 

 ly. Since this fact has been fully established the cus- 

 tom has been to put out the young fish within a few 

 days after hatching. They are shipped in carload lots 

 of three to four millions to the various lake ports 

 reached by rail, where they are put upon tugs and con- 



