Age andl growth of the flathead, platycephalus indicus, from the coastal waters of west kyushu, Japan

摘要

The ages of flathead (Platycephalus indicus; Japanese name: magochi), sampled from coastal waters of west Kyushu, Japan, were determined from transverse sections of otoliths. The following two methods were used for age validation: (1) monthly change in marginal increments of 503 sectioned otoliths sampled from the waters, and (2) counting of opaque zones on sectioned otoliths of 28 known-age fish artificiallly fertilized and reared during one to 9 years at two fisheries research laboratories in Japan. The former method revealed that one annulus was formed per year during early summer months. The latter one also validated one annulus per year. Assuming a birth date of June 1 from the monthly change of gonadosomatic indices, ages were assigned to every individual according to the number of opaque zones. These ages were then fitted to the von Bertalanffy growth equations. Equations obtained were L_t=430.3(1-exp(-0.667(t+0.093))) for males, and L_t=551.5(1-exp (-0.478(t+0.125))) for females, where t is age (year) and L_t the total length (mm) at age t. Maximum age observed was 16 years for males and 11 years for females, and the length of females calculated from the equation was larger than that of males at any age.