KNUT DAHL. 



This fact in connection with the varying conditions of nu- 

 trition, which undoubtedly occur in the rivers, will inevitably 

 cause the fry of each year to represent a series of different 

 stages of development. Thus a phenomenon like the emigra- 

 tion, which evidently is dependant on a certain stage of deve- 

 lopment, can only be realised during a longer space of time. 



Evidently no large error is committed if the age of the 

 emigrating young salmon is valued at IV4 years. 



Undoubtedly it would be important to know how long time 

 is required before these young, as grilse, return to our fiords 

 or rivers. A final solution of this question I am unable to 

 present. Conclusions as to the progress of growth of the young 

 salmon, cannot directly be based on my rearing-experiments. 

 Only when we are able to fish large numbers of small salmon 

 after emigration will a final knowledge as to the growth of 

 young salmon be obtained. However I feel obliged to com- 

 municate my experiences as to the growth of the fish in my 

 aquaria, and by means of a comparison with known facts, 

 endeavour to prepare a representation of the rate of growth of 

 the fish, which at the present time may be considered most 

 probable. In the adjoined graphical representation (Fig. 2) I have 

 drawn curves reduced to forms representing the size of the fish, 

 and with figures denoted their probable age. 



The upper one of these curves or groups represents the size 

 of the young salmon when introduced into my aquaria. In con- 

 sequence their age, estimated at IV4 years, cannot possibly be 

 lower. The lowest group represents the lowest values of the 

 grilse group as found in our waters during summer. Only the 

 lowest part of this curve is drawn, and it is compiled according 

 to Mr. Landmarks report for 1891 — 1896 in which paper suf- 

 ficient evidence is given as to the fact that the grilse consti- 

 tutes a separate annual class or group of growth. 



The middle group denoted by an unbroken fine, represents 

 the size of the young salmon reared in my aquaria and killed 



