296 BULLETIN OF THE BUREAU OF FISHERIES 



could not be relied upon with certainty and therefore proceeded to search for other 

 criteria. In doing so he discovered the fundamental principle underlying the method, 

 later devised by Dahl and Lea, of calculating the length of a fish for each year of 

 its life by the proportionate width of the bands on its scales. Walter found that the 

 relative width of a year zone on a scale expressed to a certain degree the relative 

 intensity of body growth, designated in terms of length and height. 



As Walter's paper is seldom referred to and his highly significant contribution 

 to the scale method seems to have been overlooked, I quote him verbatim (p. 108): 



Im Durchmesser des Vorder- und Hinter-feldes musz also das Langenwachstiim, in demjenigen 

 der Seitenfelder das Hohenwachstum sich widerspiegeln. Die Verhaltnisse der einzelnen Jahres- 

 felder und der verschiedenen TeOe desselben Jahresfeldes zu einander werden uns deshalb ein 

 getreues SpiegelbOd des betreffenden Wachstunis geben. Unter normalen Verhaltnissen und bei 

 rationeller Zuchtmethode ist der Langen- und Hohenzuwachs im zweiten Lebensjahre weitaus am 

 groszten, deshalb musz auch das zweite Jahresfeld der Sohuppe die groszte Breite besitzen. Von 

 da ab nimmt bei iiber-wiegendem Breitenwachstum das Langen- und Hohenwachstum bestandig 

 ab, mit ihm auch die Breite der folgenden Jahresf elder der Schuppe. Wir konnen alsobereitsaus 

 der relativen Breite der einzelnen Jahresfelder bis zu einem gewissen Grade auf die Intensitat des 

 VVachstums innerhalb der verschiedenen Jahre scMiessen, und ganz besonders ist das der FaU beim 

 ersten und zweiten Jahresfelde, in welchen ja nur das Langen- und Hohenwachstum zum Ausdruck 

 gelangt. 



Walter emphasized the fact that the growth of a scale in length is correlated 

 with the growth of the body in length and not, as Hoffbauer stated, with the growth 

 of the body designated in terms of weight. 



Thomson (1904) recorded some observations on the scales of a young whiting 

 {Gadus merlangus) held captive from May, 1902, to July, 1903 (age, 1 year and 4 or 

 5 months). The specimen grew from 10 or 20 millimeters (0.4 to 0.8 of an inch) to a 

 length of 8J/^ inches. It was "fed regularly from the hand." No winter ring was 

 recognizable in its scales at the time of death. Thomson attributed this absence of 

 an annulus to the fact that the fish was supplied with food regularly. 



Johnston (1905) presents photographs of scales taken from hatchery salmon 

 {Salino solar) 1, 2, and 3 years of age. After describing the scales of the 1-year 

 salmon and comparing them with the scales of the 2-year fish he observed that 

 "the growth of the first year is easily distinguished" in the latter and that "the 

 new season's addition is marked by a wider separation of the lines at the periphery 

 of the scale." In the scales of the 3-year salmon retained in a fresh-water pond 

 "the growth of the first and second years can be made out, but the lines of the latter 

 are not so easily distinguished from those of the third year." In a second experiment 

 Johnston (1907) again found that artificially reared salmon 2 years old had completed 

 two annuli on their scales. 



Salomon (1908) found two distinct summer growth zones in the jawbones of an 

 artificially reared and well-nourished river trout (Huche) 0.90 kilogram in weight 

 and 1 ]^ years of age. 



Dahl (1910) studied hatchery salmon and trout of known age and known life his- 

 tory and concluded, as Johnston, that "the markings on their scales corresponded 

 exactly with the seasons durmg which the fish have lived," and that the age deter- 

 mined from the scales agreed with the known life of each individual. Dahl's speci- 

 mens hatched in five different years ranged from 1 to 3 years in age. 



