Comparison of ages, morphology and osteology by birth months of larval Japanese flounder settling at Yanagihana Beach, Nagasaki Prefecture, Japan

Age, morphology and osteology of larval Japanese flounder settling at Yanagihama Beach, Nagasaki Prefecture in 1990 and 1991 were compared among birth months. Age and size at settlement (H stage larvae) decreased as the season advanced; from 25.2 days and 12.0 mm SL to 20.4 days and 9.9 mm SL in the February and April cohorts, respectively, in 1990. Then from 27.0 days and 11.3 mm SL to 22.1 days and 9.5 mm in the February and April cohorts, respectively, in 1991. Whereas no differences in morphometry and meristic counts of larvae were seen between monthly cohorts, the degree of vertebral ossification at settlement was greater in the February cohort than in the April cohort, suggesting inferior swimming ability in the latter.