In this study we investigated sex change and the mating system of a platycephalid fish, Platycephalus sp. 2 (Japanese name: Magochi), found in Japanese waters. Among 202 specimens from Tateyama, Chiba, Japan, obtained in 2014 and 2015, histological observation of the gonads distinguished 103 females, 97 males and two hermaphrodites (individual with both ovarian and testicular parts). Females were significantly larger than males. In a rearing experiment conducted with six males and three females, only the smallest male changed sex to female, thereby revealing protandry in this species. In field observations, seven males and eight females appeared throughout the study period. During pairing, a male would follow a female on the sandy bottom. The mating system of this species has been regarded as random mating based on temporal pair bonding, no territoriality, and no size-assortative mating, which correspond well with the size-advantage model. In a previous study Platycephalus sp. 2 was regarded as a gonochore, with a higher growth rate for females than males. Thus, females should be larger than males. In the present study, there was no significant difference in age between the sexes, as estimated from the number of opaque zones in sagitta otoliths. Overall, these findings indicate that there are primary females and males without sex change. Thus, protandrous and gonochoristic individuals may co-exist in populations of Platycephalus sp. 2.

在这项研究中，我们调查了鳞状鱼类Platycephalus的性别变化和交配系统sp。2（日语名称：Magochi），见于日本海域。在2014年和2015年从日本千叶县立山市获得的202份标本中，对性腺进行的组织学观察可区分出103例雌性，97例雄性和两个雌雄同体（分别有卵巢和睾丸部分）。女性明显大于男性。在对六头雄性和三头雌性进行的饲养实验中，只有最小的雄性改变为雌性，从而揭示了该物种中的脯氨酸。在实地观察中，整个研究期间出现了7位男性和8位女性。配对期间，雄性会在沙质底部跟随雌性。该物种的交配系统被认为是基于时间对键合的随机交配，没有地域性，也没有大小可分的交配，这与尺寸优势模型非常吻合。Platycephalus SP。2被认为是一个生殖腺，雌性比雄性有更高的生长率。因此，女性应大于男性。在本研究中，根据人参耳中不透明区域的数量估计，性别之间的年龄没有显着差异。总体而言，这些发现表明，有原性别的未婚男女。因此，雄性先熟和集群个人可能在人群共存Platycephalus SP。2。