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 
