16 THE AGE AND GROWTH OF SALMON AND TEOUT. 



suitable conditions of nourishment. It is, however, the fact that not a 

 single salmon had its scales unaffected by its stay in the river and the act 

 of spawning, and therefore, of all the fish examined every single one would 

 throughout its future existence show on its scales absolute indications of 

 having spawned. 



I consider it therefore as absolutely proved that practically every single 

 fish which survives the act of spawning, and again regains the feeding 

 grounds of the sea, will possess a " spawning mark," and it equally follows 

 that the occurrence or non-occurrence of this mark may be utilised as a fairly 

 certain indication as to whether a fish has previously spawned or not. 



2. THE SCALES OF TROUT. 



The scales of all varieties of trout show a very close resemblance to 

 the structural conditions and peculiarities previously described in relation 

 to the scales of their near relation, the salmon. I will therefore avoid any 

 lengthy description, but will briefly mention a few of the main points which 

 are of importance for the investigation of trout scales. 



The formation of the scale begins about midsummer, in the first year 

 of its life, and, as is the case with salmon by the formation of a minute 

 plate. As this plate increases in size concentric growth-rings are formed 

 around the edge in the same manner as with salmon. 



Some examples of young trout caught in August, 1907, in a Nordland 

 stream, showed the following maximum number of growth-rings on the 

 scales : 



Of 2 individuals, 8*2 8*8 cm., 1 ring (small plates). 

 1 8'5 cm., up to 2 rings. 



1 8'5 cm., 8 



4 3'7, 8'8, 3-8, 3'9 cm., up to 4 rings. 



1 8'8 cm., up to 5 rings. 



1 4'0 cm., 6 



In summer the rings are farther apart, and in winter closer together, 

 and more branched, and similar to what was described in connection with 

 salmon. 



We can prove this by examining scales from fish caught at different 

 seasons of the year, and also by studying artificially-reared fish of known 

 age. I have examined several examples of artificially -reared fish, and have 

 found that the markings on their scales correspond exactly with the seasons 

 during which the fish have lived. As an example I have given two 

 illustrations of the scales of these fish (Figs. 20 and 21). 



When we compare the growth-zones and the consequent age of the fish 

 as shown by the scales, we find that in each case this is in complete 

 agreement with the known life of each individual. 



