Robertson. — Hatching Fry in Gravel 149 



it hastens the incubating period and compels the liberation of fry- 

 in the late winter when food is at its minimum, but it is reasonable 

 to presume that in springy localities the same temperature that 

 hastens egg incubation also hastens all other forms of aquatic 

 life and food is thus automatically provided. 



In any event water of warmer winter temperature than that 

 used in the hatcheries is the natural element, and the aversion 

 to its use is based on the presumption that the temperature of 

 the running water in a stream determines the length of the 

 incubating period of the eggs that are deposited in it. This is 

 not so, however, for temperature readings taken from beneath the 

 bottom of streams, and from holes dug in the banks and bars, 

 gave temperatures as much as eight degrees higher than that of 

 the running water above, and I am also partially convinced that 

 the time of emergence of the fry is not dictated by the absorption 

 of the sac alone and may depend on the temperature of this blanket 

 of cold water above them. 



Another point in this connection I wish to emphasize is, the 

 sequence of the time of spawning of the different kinds of Pacific 

 salmon is: sockeye, humpback, spring, dog and cohoe. This 

 sequence also obtains in a general way in the comparative strength 

 of fry of these fish. Heretofore sockeye eggs, when procurable, 

 were the only salmon eggs handled in British Columbia hatcheries, 

 where their development was retarded in surface water of low 

 winter temperature, while their aggressive and less worthy 

 cousins, hatched naturally in spring water, had advanced in growth 

 sufficiently to be able to devour the sockeye fry when they were 

 liberated. 



The moral is that in the absence of good reasons against it, 

 the liberation of the fry of any species should synchronize with 

 that of the same species in nature. 



DEPOSITING THE EGGS NATURALLY. 



In depositing the eggs the action of the fish's tail scoops a 

 hollow in the gravel, and the eggs when expressed, are carried by 

 the current into the interstices. The eggs are not deposited in 

 masses, and as the fish works forward they are covered. This 

 takes place while the eggs are in the soft state, and as they harden 

 and swell they assume the shape of the interstice in which they 



