ANTERIOR SCALE MARGIN 



C IRCULI 



ANNUL 



FOCUS 



r.»'/ 



CTENII- 



-■■'..^ » /x^-^^^x^A-^-^i^^^r^z 



Fi^re 3. — The cycloid scale of a whitefish (left) and the ctenoid scale of a sunfish, 

 showing year-marks (annuli) and general scale features. Both fish were 2 years old. 



Figure 4. — A microprojector designed for the study of fish scales. The magnified scale 

 image is projected on the frosted glass screen. 



Scales may be prepared for study by mount- 

 ing the whole scales on glass slides or, more 

 commonly, by pressing imprints of the scale 

 circuli into transparent plastic. The scale 

 photographs shown are of these plastic im- 

 pressions. Scales or scale impressions are ex- 



amined under a low-power microscope or by 

 use of a microprojector like the one shown in 

 Figure 4. 



As fish grow older and growth slows down, 

 with a consequent narrowing of the band of 

 circuli added to the scale each year, it becomes 



— 4 — 



