Growth increments in statoliths of Idiosepius paradoxus were observed for aging analysis. The rate of increment formation was examined by staining the statoliths with tetracycline at 5–14 d intervals. In 6 of 16 specimens, increments formed daily, but in the other specimens, increments formed less than one per day. The maximum number of increments observed in males and females were more than 150 and 140, respectively, suggesting a life span of ≥150 and ≥140 d. During the cool season (from November to April), the dorsal mantle length (DML) and the number of increments gradually increased. Specimens collected in June showed bi-modal patterns in DML and the number of increments. Only small specimens were collected from August to October. These results suggest that two generations alternately occurred in the cool season and in the warm season.
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