||This study investigated life-history traits of the Japanese flathead, Inegocia japonica, inhabiting the waters off southwestern Taiwan. A total of 1,557 I. Japonica specimens (701 females, 619 males, and 237 individuals of unknown sex) were collected in the fish markets of Keziliao and Donggang during the period from January 2012 to April 2013 and in January 2015. The size (total length, TL) of specimens ranged from 15.4 to 28.2 cm for females, and the size from 12.8 and 25.4 cm for males. For the sex-unknown specimens, their TLs ranged from 10.2 to 25.4 cm.|
Seawater temperature is suggested to be an important environmental factor affecting the reproduction of I. japonica. The investigations of gonodo-somatic indices (GSIs) and histological sections of ovaries indicated that the I. japonica population inhabiting in waters off southwestern Taiwan spawns year around with a peak spawning period from January to April. The average fecundity was 83,442 (±36,619) eggs, estimated by counting the numbers of oocytes in the most advanced size group from the ovary samples of seven mature females. The smallest TLs at sexual maturity were 16.6 cm (0.7 years) for females and 15.0 cm (0.36 years) for males. Hermaphroditic individuals undergoing sex change were difficult to be properly separated from males through naked eye examination of gonad appearances. Based on histological examination of gonad samples, this study found that hermaphroditic individuals, which had pink color and more visible blood vessels in the appearance of gonads, produce male function.
Ages, revealed by otolith interpretation, of I. japonica ranged from 0.5 to 4.5 years.
The otolith ring, analyzed by marginal increment, formed annually during the period from October to December (autumn and winter). Compared with other species of Platycephalidae, I. japonica exhibits a short-lived species (mean age: 2.5±0.8 years) with a fast growth rate (0.76 year−1).