Identification of Pacific Salmon and Steelhead Trout 

 by Scale Characteristics^ 



By 



KENNETH H. MOSHER, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Seattle, Washington 98102 



ABSTRACT 



Descriptions and illustrations of the scales of each species, a key to identifying 

 species by use of scale characters, and a section on the appearance of juvenile sal- 

 mon scales are presented. 



INTRODUCTION 



Identification of species of salmon (genus 

 Oncorhynchus ) and steelhead trout ( Salmo 

 gairdneri) in the sport and commercial catch 

 of the Pacific coast is important in assessing 

 the relative production and value of 

 each species and in performing biologi- 

 cal research. 



Methods of identifying the species from the 

 examination of whole or gutted fish are avail- 

 able; however, at times it may be necessary to 

 determine the species from a portion of a fish 

 such as a steak or fillet. Any scales on these 

 portions offer a means of identification. 

 Although Koo (1962b) and Bilton, Jenkinson, 

 and Shepard (1964) have published on identifi- 

 cation of species of Pacific salmon by scales, 

 the masu salmon (O. masou ) and the 

 steelhead trout were not included in their 

 studies. 



This illustrated guide has been prepared to 

 show the differences among scales of species 

 of Pacific salmon and steelhead trout. With a 

 minimum of preinstruction, fishery inspector s 

 in the field or on shipboard can use this guide. 

 The species differ from each other in their 

 life histories, and some scale features clearly 

 show certain aspects of these life histories. 

 The paper is organized as follows: The gen- 

 eral scale features are described, then each 

 species is described separately, with photo- 

 graphs of scales of postjuvenile fish (fish that 

 have lived in the ocean for some time); a key 

 to identification of species of postjuveniles by 

 scale characters; a section on identification of 

 juvenile fish (from the time scales first appear 

 on the fish body until the fish migrates to the 

 sea); and finally a glossary of terms used in 

 these studies. 



CHARACTERS OF SCALES USED FOR SPECIES IDENTIFICATION 



In the following sections various subjects 

 bearing on the use of scales for identification 

 of species will be discussed: 



1, The visual appearance of the scales, 

 including the growth features of the an- 

 terior field which are used in determina- 

 tion of age of the fish, and the features of 



the posterior field which assist in identi- 

 fication of species. 



2. Life history features that are re- 

 vealed by the scales of the various species 

 and behavioral patterns that influence the 

 utility of age and other characters for 

 identification purposes. 



This paper Is based on one by J. T. Barnaby and A. C. Delacy, [no date, but circa 1944], Identification of Pacific 

 salmon and steelhead trout by means of scale examination. U.S. Fish Wildl. Serv., Seattle, 3 pp. (processed). Copy is 

 available at Bureau of Commercial Fisheries Biological Laboratory, 2725 Montlake Boulevard E., Seattle, Wash. 

 98102. 



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