KIMURA and SAKAGAWA: SCALE PATTERNS OF PACIFIC SARDINE 



Table 1. — Results of aging of 205 known age, laboratory-reared sardines from scales. 



Table 2. — Frequency and percent (in parentheses) of Pacific sardines with various 

 number of scale marks, as determined from scale reading. (Sardines were reared 

 in the laboratory for 24 months.) 



by a condition factor (MacGregor, 1959). The 

 factor (K) is calculated as a ratio of the weight 

 in grams (W) to the cubic power of length in 

 millimeters (L): K = (W/L^) x 10^. 



Back-calculated lengths from scale measure- 

 ments were derived by two methods. Method 

 one was by direct proportion, Lm = (Sm/Sr)L, 

 where Lm = back-calculated length at time of 

 mark (m) formation, Sm = scale width from 

 focus to mark m, Sr —' scale width from focus 

 to margin, and L = length at sampling. Meth- 

 od two was also by direct proportion but with a 

 correction factor (c) for body length when 

 scales first increase in size in the Pacific sar- 

 dine. The method uses the equation Lm = c + 



(Sm/Sr) (L — C). 



ACCESSORY MARKS AND ANNULI 



FREQUENCY OF OCCURRENCE 



An annulus is generally believed to form at 

 annual intervals, usually as the result of a slow- 

 ing down in growth such as occurs in winter for 

 temperate species. An accessory mark, on the 

 other hand, is believed to occur, if at all, at ir- 

 regular intervals (Walford and Moser, 1943), 

 the causes of which are unknown. 



We examined the scales of the laboratory- 

 reared fish and were unable to distinguish be- 

 tween the two types of marks. To test if other 

 scale readers similarly could not distinguish ac- 

 cessory marks from annuli as we did, a series of 

 scales from the laboratory-reared fish was mixed 



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