^44 KNUT DAHL. 



and day. In this respect it has been very instructive to let a 

 trout of corresponding size down to the salmon. 



All day through I could then see the trout remain nearly 

 in the same place su-pended in midwater, while the shool of 

 young salmon lively svimming constantly circulated round the 

 aquarium. Specially striking has also been the different way 

 in which their appetite asserts itself. 



The appetite of the trout is not strong every day. Often 

 it will assert itself only within intervals of several days. Given 

 the opportunity to eat as much as they like the trout will then 

 gorge themselves until the food hangs out of their mouth, yes 

 even to such a degree that they will drop to the bottom and 

 motionless digest for several days. 



The salmon eats as a rule several" times every day. They 

 do not gorge themselves to the same degree as the trout, and 

 they digest very rapidly. Thus after the lapse of a few hours 

 they are very often prepared for a new meal. 



Respecting the colours a considerable difference has been 

 noticeable in the two species. 



Excepting the gradual disappearance of the parr marks and 

 the red lateral spats, the colour of the salmon has not changed. 

 During the whole time I have kept them they have been of a 

 strong shining sivercolour with a blueish green undercoating on 

 the head and back, a few large black spots scattered mainly on 

 the dorsal side of the body. 



When exposed to strong light, their colours have paled a 

 little resuming their ordinary hue as soon as the light was 

 subdued. 



The trout have been quite different. Even the most shining 

 and silvery trout, taken directly from the sea, have very soon 

 assumed quite other colours varying in blue, blueish green brown 

 and yellow. Also they have always grown very much spotted. 

 These changes have also taken place when trout of the same 



