Binan Surveying and Designing K.K., Tamano, Okayama 706-0021, Japan
Age, growth and maturity of the Japanese sardinella Sardinella zunasi were estimated from scale readings, observations and measurements of gonads. Specimens were collected by angling and set net as well as from commercial landings. Scale rings were found to be formed once a year from September to October. The matured are at least 9.5 cm in standard length for both sexes and the spawning season extends from June to September and its peak is in August. By applying the maximum likelihood method to the standard length-at-age data, we found that von Bertalanffy's growth equation with seasonal changes is a better fit than any other type of growth model, i.e. SLt=12.53[1-exp {-0.6254(F(t)+0.534)}] F(t)=t-(1/2π) sin 2π(t-0.259) for males, and SLt=13.42[1-exp {-0.4990(F(t)+0.713)}] F(t)=t-(1/2π) sin 2π(t-0.287) for females, where SLt is standard length in cm and t is age in year. The growth of females is statistically higher than that of males. SLs at which 50% of specimens attain maturity were estimated by logistic analysis as 10.11 and 10.32 cm for males and females respectively.