THE AGE AND GKOWTH OF SALMON AND TEOUT. 



winter rings are present, showing the commencement of the third winter of 

 the fish's life. 



The beginning and the duration of winter naturally vary in different 

 rivers and districts, and consequently there will be considerable variation 

 in the formation of the broad rings indicating summer growth. It seemed 

 to me for the present to be unnecessary to devote much valuable time to the 

 investigation of fish from numerous localities in order to establish this fact. 

 What I considered of more importance, as I have endeavoured briefly to 



prove, was that the growth of the 

 parr is very different in summer 

 and winter, and that the seasons 

 leave ineffaceable marks on the 

 scales, which consequently enabled 

 one to state the number of winters 

 and summers which the fish has 

 spent in the river. 



(b.) The Scale after Migration to 

 the Sea. 



When the parr becomes a 

 smolt and migrates from the river 

 to salt water it meets with abso- 

 lutely different conditions. In 

 what manner are these conditions 

 indicated on the scales ? 



In order to illustrate this 

 question I give a drawing of por- 

 tion of a scale of a young salmon 

 (Fig. 7). This fish was caught as 

 a smolt with many others at the 

 mouth of the Gula Eiver at the 

 end of June, 1900. It was then 

 between 10 cm. and 15 cm. long. 

 Together with others it was placed in a large salt water tank at the 

 Trondhjem Biological Station, and kept there until October 18, 1901. 

 When it was killed it was 29'5 cm. in length. 



Naturally the surroundings one could give it were not so favourable as 

 it would have obtained in the sea, but in spite of this it had grown much 

 more rapidly than any parr living at liberty in fresh water would have done. 

 In the portion of its scale shown in Fig. 7 we clearly see the three winter- 

 bands denoting its life in the river as a parr. Immediately after the com- 

 pletion of the third winter the fish was placed in the aquarium, and the 



FIG. 6. Parr 12 cm. Softeland middle of 

 October, 1908 (magnified). 



