62 MARVELS OF FISH LIFE 



long it remained in the sea, and at what age, or ages, 

 it returned to fresh water to spawn. 



If the scale of a smolt taken in fresh water on its 

 way to the sea be examined, about twenty-six of these 

 rings will be found to be present. 



The growth of the young fish during its life in fresh 

 water as a parr is slight, so the rings are very narrow, 

 though the difference between summer and winter growth 

 can be easily recognised. If the same smolt is captured 

 after it has been only a few weeks in tidal waters, out- 

 side the narrow rings formed in fresh water will be seen 

 two or three broad rings. These broad rings are formed 

 in consequence of the immediate rapid increase in size 

 of the smolt as a result of his more abundant food supply 

 in tidal water. During his first year in the sea the fish 

 continues to add broad rings of growth, which gradually 

 approximate each other as the winter approaches, and 

 this process is repeated year by year so long as the 

 salmon remains in the sea. 



Not only can the age of a salmon thus be read, but 

 it also is possible to tell at what age a fish returned to 

 fresh water to spawn. This is shown by a scar or spawn- 

 ing mark on the scale, which takes the same crescentic 

 shape as the rings of growth. 



The spawning mark is formed in consequence of the 

 fact that when a fish has spawned, it loses weight and 

 its skin shrinks, but the scales cannot shrink, and so the 

 edges fray. When the scale again grows, the frayed edge 

 leaves a permanent scar. 



