SMOLTS 13 



earlier than the height of the spawning season in 

 the latest river, viz., December 8. Of course, in all 

 districts one may find the spawning season extend- 

 ing over a long period if the very latest pair of 

 spawners are taken into account, and exceptionally 

 early or exceptionally late fish spawners caused, it 

 may be, in great measure by the presence or absence 

 of frost may account for a great deal of the diversity 

 seen in the sizes of parr at any one season, but the 

 chief periods of spawning have to be reckoned with 

 in estimating the period of the smolt's average stay 

 in fresh water. 



The temperature of the water materially controls 

 the length of time between impregnation and hatch- 

 ing, and various experiments have been tried to 

 ascertain on the one hand how soon hatching may 

 be brought about and too early hatching is natur- 

 ally accompanied by a constitutional weakness of the 

 alevins and on the other hand how long hatching 

 may be retarded, so that eggs may be safely sent to 

 the Antipodes. Such points are of practical import- 

 ance to the fish culturist, but under natural condi- 

 tions in this country hatching may be expected to 

 take place in from ninety to 100 days, in tempera- 

 tures varying from 40 to 45 F. If the water 

 temperature is constantly kept on the verge of 

 freezing point (32 F.) hatching is retarded for about 

 148 days. If the eggs are frozen, or encased in ice 

 in a closed vessel, they die : oxygen must be taken 

 in and carbonic acid given off; the young salmon 

 even inside the egg must have the power to respire. 

 In like manner, if the eggs become coated with any 



