TROUT 



as they usually do, but swim about on their 

 backs at the surface, with part of the yolk-sac 

 out of the water. An effectual cure for this is 

 to put the affected alevins into still water for 

 about thirty-six hours. I have observed this 

 affection in the alevins of the rainbow trout 

 (Salmo irideus), the common trout (S. fario) and 

 the Quinnat or Calif ornian Salmon (Onchoryn- 

 chus conicha). 



"Blue Swelling" of the yolk-sac is another 

 disease from which alevins sometimes suffer, but 

 I have never heard of any cure for this. Another, 

 " paralysis," may be caused by lack of sufficient 

 current and by insufficient aeration of the water. 

 Sickly alevins will, as a rule, drop out of the 

 pack, and lie on the bottom or against the end 

 of the hatching tray, where they are carried by 

 the current. 



Dead alevins should be removed at once, and 

 for this reason it is necessary that the hatching 

 trays should be examined at least once a day. 



41 



