ON TROUT. 



65 



On again examining Table XXVII. we find all the information we 

 need regarding the age and growth of Mj0sen trout subsequent to migration. 

 I have put in brackets the fish whose scales had spawning marks. In the 

 Chapter on " Methods " I mentioned that these spawning marks in trout 

 do not seem to occur with the same regularity as they do in salmon. As, 

 however, the surface of trout scales is comparatively small, it often happens 

 that the spawning marks cannot be deciphered with any degree of certainty. 

 Consequently I have not ventured to draw up an analysis of trout with 

 spawning marks as a means of determining the average length and weight. 

 The average length and weight has accordingly been based solely on the 

 investigation of those scales which did not possess any spawning marks. 

 On the other hand, when investigating the question of age, I have noted in 

 brackets the fish with spawning marks, and it is therefore possible that the 

 age in some cases may be slightly underestimated. 



If we now sum up the information we have obtained from Table XXVII. 

 we get the following comparative statement : 



What chiefly strikes us in this statement is that we are dealing with 

 fish which attain a much higher age after change of growth than either 

 salmon or sea trout. While in the case of these latter, one rarely meets 

 with fish which have lived more than three or four winters after migra- 

 tion, or change of growth, the Mj0sen trout attain to far higher ages. 

 No doubt the number of individuals decreases with advancing age, still 

 there must be quite a considerable proportion of the stock which are of 

 great age. 



The average lengths and weights of the different year-classes teach us 

 that growth is vigorous even at a very high age, and the ultimate lengths 

 and weights of Mj0sen trout resemble the values characteristic of salmon 

 which have spent three winters in the sea. 



The scales of Mj0sen trout, moreover, exhibit a peculiarity which is 

 much more pronounced than in any other district in Norway which I have 

 investigated, though probably it will be found to occur in many other inland 

 waters. If we look at the scale depicted in Fig. 23 (Plate VIII.) we notice 

 that the last winter-zone lies very near the edge. When the fish was caught 

 S.T. 5 



