CAUSES OF VARIETY IN TROUT. 223 



twentieth fish I have taken in an hour, and 

 it is a grayling of at least fifteen inches long ; 

 and there is a trout of eighteen, and several 

 salmon trout, which look as if they had run 

 from the sea. 



Hal. — These salmon trout have run from 

 a sea, but not from a salt sea ; they are fish 

 of the Traun See, as it is called by the Ger- 

 mans, or Traun Lake, which is emptied by 

 this river. 



Phys. — Tell us why they are so different 

 from the river trout, or why there should be 

 two species or varieties in the same water. 



Hal. — Your question is a difficult one, 

 and it has already been referred to in a 

 former conversation ; but I shall repeat what 

 I stated before, — that qualities occasioned 

 by food, peculiarities of water, &c. are trans- 

 mitted to the offspring, and produce varieties 

 which retain their characters as long as they 

 are exposed to the same circumstances, and 

 only slowly lose them. Plenty of good food 

 gives a silvery colour and round form to 

 fish, and the offspring retain these .charac- 

 ters. Feeding on shell-fish thickens the 



