Reproductive cycle, age, and body size at maturity and fecundity of female willowy flounder Tanakius kitaharai

Annual reproductive cycle, age and body size at maturity, and potential and relative fecundity were examined in female willowy flounder in the North Pacific off Japan. Vitellogenesis became active from September, followed by the beginning of spawning in December. The spawning season continued until May with its peak in January. Estimated maturation rate was 50% at a standard length of 16 cm, 30% in 2‐year‐olds, and almost 100% in ≥ 3‐year‐old fish. Potential fecundity increased with age, while relative fecundity decreased in older fish. The results clarify some aspects of the detailed reproductive biology of female willowy flounder and emphasize the importance of age‐composition data in estimating reproductive potential within a population.