CAUSES OF VARIETY IN TROUT. 261 



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 Tr au n Lake, which is emptiedby 

 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 for- 

 mer conversation ; but I shall repeat what I 

 stated before, that qualities occasioned by 

 food, peculiarities of water, &d. 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 much on larvae and on shell- 

 fish thickens the stomach, and gives a brighter 

 yellow to the belly and fins, which become 

 hereditary characters. Even these smallest 

 salmon trout have green backs, only black 

 spots, and silvery bellies; from which it is 

 s 3 



