A STUDY ON TROUT AND YOUNG SALMON. 277 



These fry abide in the river until reaching a certain size, 

 when, acquiring the silvery coat of the emigration stage, it leaves 

 the river. 



My investigations showed that, as a rule, the size of the 

 emigrating young salmon of our rivers varies from 9 — 13 cm. 

 (Vide Tab. IV). In the following pages I will endeavour to 

 throw some light on the question of the age of these fishes, 

 counting their age from the time of hatching, viz. ca. April 1. 

 Most authors, who have treated the system as well as the bio- 

 logy of the salmon, agree quite unanimously that the young 

 salmon (smolts) emigrate from the rivers during spring (April, 

 May) in schools. This is described as a phenomenon limited to 

 a relatively short space of time. 



The general idea seems to be, that the young salmon at a 

 certain time of the year is suddenly smitten with the migratory 

 instinct, resulting in an emigration in masses analogous to the 

 migration of our migratory birds. 



When, during the first summer of my investigations I found 

 in the latter half of August emigrating young salmon in the 

 mouth and lower parts of the Gula, I was consequently not a 

 little surprised. These young fish were not in the least different 

 from the emigrants of spring (Vide Tab. IV col. 3). 



This experience has been confirmed by all later investi- 

 gations. At any time during summer I have been able to prove 

 the occurrence of young emigrating salmon in the mouth and the 

 lower parts of the Gula as well as the Orkla. 



In order to gather experience on the occurrence of young 

 salmon in the different stages of development right from the 

 spawning places down to the sea I effected a series of fishing 

 experiments in the river Orkla, from the river mouth up to 

 the spawning beds in Meldal. On the 16*"^, 17*^ and 18*^ 

 of July 1901 I fished with the rod at the following localities: 

 Kalstad (Meldal ca. 40 km. from the river mouth), Aarlivold 

 (20 km. lower down), Bak, Forve, and the mouth of the Orkla, 



