OBSERVATIONS ON SCALE PATTERNS AND GROWTH OF THE 

 PACIFIC SARDINE REARED IN THE LABORATORY 



Makoto Kimura and Gary T, Sakagawa^ 



ABSTRACT 



Scale patterns and growth of Pacific sardine (Sardinops caerulea) were studied with lab- 

 oratory-reared fish held for 24 months. All scales examined after the fourth month had 

 accessory marks. The first accessory mark was formed in August to October and the 

 second accessory mark, in May to August. The accessory marks were indistinguishable 

 from annuli that formed in November to March. 



Five possible causal factors of mark formation were investigated — temperature, sa- 

 linity, gonad index, condition factor, and relative growth rate. Growth rate showed the 

 best correlation. The accessory mark was formed during a period of change in growth 

 rate and the annulus during a period of relatively constant growth rate. 



An estimate of the body length-scale radius relation indicated that scales first increase 

 in size at a body length of 33 mm. 



Growth in length was rapid from the start of the experiment to the fourth month, after 

 which the increase was gradual. The average instantaneous rate of growth was about 

 0.47/month during the first 4 months and about 0.03/month thereafter. 



It was concluded that the abrupt increase in Lj that was recorded in the 1940's for the 

 sardine population was probably caused by errors in aging, owing to a change in scale 

 readers and scale-reading criteria. The ages of fish age II and older were probably 

 underestimated by the recent scale readers. 



In the course of aging Pacific sardine (Sardinops 

 caerulea) from scales, the senior author ob- 

 served, from comparison of back-calculated 

 lengths with growth curves, that accessory 

 marks or false annuli occurred frequently and 

 were easily mistaken for true annuli. This was 

 contrary to the findings of Walford and Mosher 

 (1943:8-9), who reported that the annulus was 

 "present on all normal scales of an individual" 

 whereas an accessory mark was only rarely pre- 

 sent on "all the scales of an individual." Since 

 misidentifying an accessory mark as an annulus 

 can aflfect the estimated age of a fish, a labora- 

 tory experiment was conducted to determine (1) 

 the frequency of occurrence of accessory marks, 



(2) the time of accessory mark formation, 



(3) possible factors that may cause accessory 

 mark formation, (4) the time of annulus for- 

 mation, and (5) the seasonal pattern of sar- 



' National Marine Fisheries Service, Southwest Fish- 

 eries Center, La JoUa, CA 92037. 



dine growth. The experiment was initiated in 

 May and was terminated approximately 24 

 months later. Results from the first 12 months 

 of the experiment were reported by Kimura 

 (1970) , who showed that an accessory mark was 

 present on scales of 4.5- to 5.0-month-old fish. 

 This report is a more comprehensive presenta- 

 tion of results from the entire experiment. 



METHODS 



REARING 



The collection of sardine eggs and the hatch- 

 ing and rearing of the young in the laboratory 

 for the first 12 months were described by Kimura 

 (1970) . The general procedures, including those 

 used after the 12th month, are briefly reviewed 

 as follows. In May 1968, sardine larvae were 

 hatched from eggs collected in plankton tows ofl? 

 San Diego, Calif., and the larvae were held in a 



Manuscript accepted April 1972. 



FISHERY BULLETIN: VOL. 70, NO. 3, 1972. 



1043 



