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 seales cannot shrink, and so the 
edges fray. When the scale again grows, the frayed edge 
leaves a permanent scar, 
