INTRODUCTION. ix 



For comparison with our own fish I obtained from Denmark and 

 Bavaria examples of trout, some captured in their wild state and others 

 artificially reared. Some of these I collected myself in the course of 

 a short journey during the autumn of 1909, and the rest were sent to me 

 later. In this connection I have to thank Herr Smidt-Nissen of Ejstrup, 

 Herr Pedersen of Vamdrup, the Bavarian Fishery Association, and 

 Dr. Plehm of the Eoyal Bavarian Fishery Experimental Station in Munich, 

 who was kind enough to collect samples for me. 



I likewise collected during my travels a few small samples of char and 

 grayling for purposes of comparison. 



As regards the collection of material, I desire further to state that each 

 fish was as a rule weighed and measured, and where possible the sexual 

 organs were also examined. The data thus obtained were written down on 

 an envelope in the case of every fish, and a sample of its scales was scraped 

 off and placed inside the envelope in which they were dried. The sample 

 of scales was taken whenever possible, from above the lateral line and a 

 little behind a perpendicular line drawn from the posterior edge of the 

 dorsal fin. 



The length of salmon was always measured by taking a line from the 

 tip of the upper or lower jaw to the end of the median ray of the caudal fin. 

 This method of measurement was adopted so as to accord with the previous 

 measurements of salmon taken in Norway. 



In the case of trout and other fish it was found necessary for various 

 reasons to measure the length from the tip of the snout (upper or lower 

 jaw) to a perpendicular line drawn between the flukes of the caudal fin when 

 spread out naturally, that is to say I employed the method adopted by 

 Heincke for measuring herrings which has since come into general use in 

 the International Ocean Eesearches for measuring all fish with forked 

 tails. 



What follows has been arranged in such a manner that all important 

 determinations of length and weight in relation to size and age are set down 

 in tabular form in the Appendix. I shall begin by discussing the method 

 employed and its possibilities, and then, by a comparison of the data con- 

 tained in the tables, endeavour to elucidate the various problems connected 

 with the age, growth, and general life-history of the different fish, in so far 

 as these are affected by the knowledge obtained from the methods adopted. 



KNUT DAHL. 



BBEOBN, 23rd May, 1910. 



