A STUDY ON TROUT AND YOUNG SALMON. 281 



sizes if I had been able to secure these smaller fishes. Then it 

 is very improbable that a smaller group exists between 2 cm. 

 and 6 cm. as late in the summer as in the middle of July. 



Consequently it becomes most reasonable to consider the 

 group in the last column as 0-group or the fry of the year, viz: 

 fry hatched ca. April 1, 1900. For the same reason it is not 

 impossible that the emigrants represented on the second last 

 column, may belong to this group which gradually, during 

 growth, migrates down the river. 



If however the results from our state rearing establishment 

 at Ullern should be a correct gauge of the normal growth of 

 the salmon fry, a group smaller than the smallest I have found 

 must exist in our rivers in summer. This fact, if existing, 

 would clearly retard emigration for one year. The emigrating 

 smolts, which leave the rivers in spring would thus be 2V4 years 

 old because they could not possibly grow from maximum 8 cm. 

 (which the reared fry reach in October) to maximum 13 cms. 

 which is peculiar to the emigrants of spring. 



Without expressing any definite opinion as to the final 

 decision on this question, I admit, that at present I feel most 

 satisfied and think the groups represented in tab. No. IV are 

 best explained, if the matter is considered from the point of 

 view, that the emigrants of spring are ca. IV4 years old („I-group"). 

 Those emigrating during summer are partly the young belonging 

 to the I-group, the fry of the previous year which have not 

 developed so quickly as those previously emigrated. These 

 emigrants of the summer also belong partly to the fry of 

 the year, or the „0-group", which in July and August have 

 grown large enough for emigration. The rest of the 0-group 

 remain during winter in the river and emigrate next sprmg 

 and early summer as „I-group". 



It seems to me that this view is feaseable considering that 

 hatching and consequently also development, have an amplitude 

 of several months. 



