The reproductive biology of female crimson sea bream Evynnis tumifrons off the southwestern coast of Kyushu, Japan

Ovarian maturation, size at sexual maturity and the annual reproductive cycle of female crimson sea bream Evynnis tumifrons were studied using samples collected from April 2012 to June 2014 off the southwestern coast of Kyushu, Japan. A total of 801 ovaries were examined histologically to estimate the degree of ovarian maturation. E. tumifrons showed an asynchronous ovary signifying multiple spawning in a single reproductive season. Ovarian maturity stages were classified into six categories based on the appearance of the most advanced oocytes, post-ovulatory follicles and atretic oocytes in the ovary as follows: immature, maturing, mature, spawned, spent and resting. Females with ovaries at maturing, mature, spawned or spent stages were defined as sexually mature individuals, and the size at sexual maturity was estimated to be 179-mm fork length based on 50% maturity size. Monthly changes in the gonadosomatic index and the occurrence of mature or spawned maturity stages showed that the spawning season lasts from November to May with an intermission in March 2013. The factor responsible for this intermission was considered to be the low water temperature that occurred in the preceding month.