Investigations were carried out by using the samples caught with set nets, seine nets, and boat seines from 1992 to 1996.
Most of the catches with set nets, operated in the near shore, were male in the early fishing season, and according with passage of fishing season the female ratio increased gradually. Eighty percent of the catches with seine nets, operated in the offshore, were female.
GSI of females was higher in the catches of the offshore than the near shore. The frequencies of the oocyte diameter showed that ovaries have a small and middle sized oocyte group, and large sized maturing oocyte groups. Ovaries of the offshore catches have large sized oocytes, and ovaries of the near shore catches have small and middle sized oocytes or the transparent oocytes remaining un-spwned at the latest spawning. Ninty seven percent of the female catches in the near shore have postovulatory folicles in the ovaries.
These results show that the male and female come to the north west coastal waters of Kyusyu in spawning season as separate groups: the male is in the near shore, the female is in the offshore. When ripened, the female go to the near shore for spawning, and immediately after spawning come back to the offshore. The spawning times of C. heterurus doederleini are thought to be at least twice during a spawning season.