642 



Fishery Bulletin 103(4) 



growth at age s6+ years and decreased at a7+ 

 years (Fig. 7). Comparisons of the relative fe- 

 cundity among age groups (1-2+, 3-4+, 5-6+, 

 and 7-8+) revealed significant differences with 

 age (ANOVA, F 3 38 =7.431, P<0.0005). In addi- 

 tion, post hoc tests (Fisher's PLSD, P<0.05) 

 revealed significant differences between the 

 following age groups: 1-2+ and 3-4+, 1-2 + 

 and 5-6+, and 5-6+ and 7-8+. The GSI and 

 BC values of individuals aged ;»7+ years were 

 also lower than those of individuals aged 5 + 

 and 6+ years, but the differences were not sig- 

 nificant (aq-test, P>0.05); however, the sample 

 size was very small; therefore the tests have 

 little power. 



Discussion 



Gonadal maturation 



GSI and histological examinations showed that 

 oocytes develop rapidly from May to August and 

 that the reproductive season lasts from Septem- 

 ber to December; mainly from September to October in 

 the study area. Mature females in the Sendai Bay area 

 were also observed for four months, but the reproductive 

 season in this area occurs from October to January and 

 peaks in November (Ogasawara and Kawasaki, 1980), 

 which was later than the peak documented in the pres- 

 ent study for the area off the Hachinohe coast. The 

 Sendai Bay catch area was located at a lower latitude 

 (37°00'N-38°05'N; Ogasawara and Kawasaki, 1980) 

 than that of the Hachinohe study area (Fig. 1); this 

 difference is relevant because gonadal maturation is 

 usually dependent on water temperature (Kruse and 



Tyler, 1983; Asahina and Hanyu, 1983; Conover, 1990). 

 In 2000, the water temperature in the Hachinohe study 

 area decreased faster than that of Sendai Bay in 1977 

 and 1978 when studied by Ogasawara and Kawasaki 

 (TNFRI 1 ). These results indicate that gonadal matura- 

 tion in Rikuzen sole also depends on water temperature. 



TNFRI (Tohoku National Fisheries Research Institute). 

 2004. Unpubl. data. Water temperature data. Tohoku 

 National Fisheries Research Institute, Fisheries Research 

 Agency of Japan. Shiogama City, Miyagi Prefecture 985- 

 0001 Japan. 



