90 FISH CULTUEE 



temperature the year round, but it ought to be 

 well aerated. Aeration must be more thorough 

 and more carefully attended to the farther the 

 water progresses towards the lower end of the 

 hatchery grounds. Trout will live and grow 

 and remain comparatively healthy, it is said, 

 in ponds where the temperature rises on occa- 

 sions to a little above seventy degrees some 

 writers say eighty degrees, provided there is 

 abundant aeration ; but water of such high tem- 

 perature is not to be desired. 



The warmer the water the shorter the period 

 of incubation. The shorter the time of incuba- 

 tion, below a certain point, the more danger 

 there is of weak fish being produced. The best 

 temperature for hatching trout eggs is between 

 45 and 50 degrees. This will make the period 

 of incubation from 45 to 60 days. A tempera- 

 ture between 50 and 60 degrees is good for 

 young and mature trout in the ponds. A lower 

 temperature is not injurious, but when it falls 

 close to the freezing point incubation is re- 

 tarded sometimes from 100 to 120 days. While 

 this is not injurious it is apt to give the fish- 



