tral zone of closely spaced circuli is often called 

 tlie nucleus. The area enclosed by the first cir- 

 culus is called the focus of the scale or the cen- 

 tral platelet. Only the first few circuli encircle 

 the focus ; the rest are arcs that do not extend 

 into the posterior field. 



POSTERIOR FIELD 



The posterior field is a relatively clear area 

 without distinctive gro\\i;h features. It photo- 

 gi'aphs black because it is unifoiTnly translucent 

 (see appendix plate 3). 



TYPES OF CIRCULI (Plate 2) 



The circuli of fresh-water and ocean growth 

 may be described as : 



1. Complete, or regular — circuli that are un- 

 broken over most of their arc. 



2. Incomplete, or irregular — circuli that are 

 broken, split, or otherwise discontinuous in 

 the anterior portion of their arc. Several 

 types of incomplete or irregular circuli may 

 be identified as follows: 



a. Broken — circuli that are broken or dis- 

 continuous in the anterior portion of their 

 arc."' 



b. Split — circuli that divide into two or 

 more circuli. 



c. Incomplete — circuli that end in a cul-de- 

 sac against anotlier one or two circuli, or 

 circuli that are not complete around the 

 anterior field of the scale. 



d. Island — a small segment of a circulus 

 that is not joined to another circulus, but 

 stands by itself. 



e. Loop — a segment of one or two circuli 

 that fomi a loop. 



f. Link — an intercomiection between adja- 

 cent circuli. 



g. Miscellaneous — circuli that are modified 

 in various other ways. 



FRESH WATER (LACUSTRINE) 

 GROWTH 



Plates 3, 4, and 5 show the fresh-water por- 



tions of adult sockeye salmon scales and give 

 examijles of zones of complete, "average," and 

 irregular circuli ; various types of winter zones ; 

 and various fresh-water ages. The same criteria 

 can be applied to scales from young salmon col- 

 lected in fresh water. 



FRESH-WATER CIRCULI (Plate 3) 



This plate shows examples of difi'erent types 

 of circuli in fresh-water gro\\i;h of ages 1., 2., 

 and 3.G See plate 2 for examples of various 

 types of circuli. Figures labeled A are scales 

 with predominantly complete circuli; those la- 

 beled B are more or less "average" scales, some 

 circuli complete, others broken and irregular; 

 and those labeled C are scales with predomi- 

 nantly broken and irregular circuli. Aitows 

 indicate end of winter growth. 



On the North American side of the Pacific 

 Ocean complete circuli generally predominate 

 on scales of fish from Bristol Bay, Karluk River, 

 Fish Creek (in Cook Inlet), Alaska; Skeena and 

 Fraser Rivers, British Columbia; and the Co- 

 lumbia River. On the Asian side of the Pacific, 

 complete circuli occur frequently on scales of 

 fish from the Ozernaia, Kamchatka, and Dalinaia 

 Rivers of Kamcliatka. 



Broken and irregular circuli predominate on 

 scales of fish collected in tlie Aleutian Islands, 

 the Alaska Peninsula, Cook Inlet (except Fish 

 Creek), and Southeastern Alaska; Smith and 

 Rivers Inlets, British Columbia; and in Blin- 

 jinaia and Bolshaia Rivers of Kamchatka. 



Fish scales from any area may have some 

 complete and some broken circuli in the fresh- 

 water zones. 



WINTER ZONES IN FRESH-WATER GROWTH 



(Plate 4) 



As mentioned previously, winter zones are 

 formed when the gro\\i;h of the scale slows do\vn 

 during the fall, winter, and early spring. The 

 circuli are formed closer together and are broken 

 or otherwise interrupted so that the winter 

 growth zone shows up as a band of circuli more 

 closely spaced than tlie adjacent circuli nearer 



5 Krogius (lySS) used counts of broken circuJi as a scale character 

 in racial studies. 



*> Age designation of salmon in reference to fresh-water life only 

 follows the recommendations of Koo (1962b) : an Arabic numeral in- 

 dicating the winters the fish spent in fresh water from hatching, 

 followed by a dot. 



PHOTOGRAPHIC ATLAS OF SOCKEYE SALMON SCALES 



247 



