Age, growth, maturity, and sex changes of monogrammed monocle bream Scolopsis monogramma in the waters around Okinawa-jima Island, Japan

摘要

Age, growth, maturity, and sex changes of the monogrammed monocle bream Scolopsis monogramma were estimated from ca. 500 specimens collected at Okinawa-jima Island in southern Japan. Age was determined from sectioned otoliths: maximum ages were 10 years for females and 9 years for males. Parameters for von Bertalanffy growth functions were L (t) = 206.6{1 - exp-0.68(t + 0.81)} (n = 337) for females and L (t) = 244.4{1 - exp-0.93(t + 0.32)} (n = 130) for males. The spawning season was estimated to last from June to July, with a peak in July. The standard length (SL) and age at 50 maturity for females were estimated as 186.4 mm SL and 3.3 years, respectively. Intersex individuals appeared from 159.6 to 237.5 mm SL (n = 16) in fish between 1 and six years old, with the highest frequencies occurring at 170 mm SL and 2 years old. Hence, almost all S. monogramma specimens found at Okinawa-jima Island exhibited pre-maturational sex change, although some may have been protogynous hermaphrodites. Biological characteristics such as age at growth, maturation, and spawning season are valuable factors that can inform the resource management of local fisheries