THE AGE AND GKOWTH OF SALMON AND TROUT. 



The points on which I thought it important to obtain further information 

 were the following : 



1. The growth of the scales of salmon-parr and smolts prior to 

 migration. 



2. The first growth of the scales in the sea. 



3. The formation of the annual rings in relation to the seasons of the 

 year. 



4. The question whether all spawning fish were so affected by their 

 stay in the river, that a " spawning mark " would invariably be found on 

 the scales of every salmon which had spawned. 



For the sake of those readers who may not have access to the publica- 

 tions mentioned, I will endeavour, even at the risk of repeating what may 

 have been previously published elsewhere, to describe the structure of the 

 scales as found by me in my investigations on Norwegian salmon. 



(a.) Scales of Parr and Smolts prior to migration. 



If we examine the scale of a smolt or parr under the microscope we see 

 at once that it consists of a transparent plate of an irregular elliptical 

 shape, and that the under surface is smooth. The anterior portion, which 

 is embedded in a pocket or fold of the skin, is characterised on the outer 

 surface by a series of concentric elliptical rings, which are parallel with the 

 outer edge of the scale. On the posterior or exposed portion of the scale, 

 and which is the only portion that is visible before the removal of the 

 adjacent and overlapping scales, these concentric lines or rings become, and 

 especially with increasing age, most irregular and indistinct. 



A good illustration of the formation and growth of the scales during 

 the first summer of the parr's life was obtained from a number of specimens 

 reared in 1898 in the State Hatchery at Haugsund, in Eker. I give below 

 the results of the examination of six selected individuals, ten to twenty 

 scales being examined in each case : 



* The scale consisted of a very small plate, the edge of which may be regarded as 

 identical with the first ring. 



