Growth, reproduction and ontogenetic migration of the greasyback shrimp Metapenaeus ensis in Osaka Bay, Japan

Abstract

To clarify the growth, reproduction and ontogenetic migration of Metapenaeus ensis, 96,898 individuals (6–175 mm in body length, BL) were collected from five areas in Osaka Bay. Larval settlement was estimated to occur from June or July to October in the Yodo River mouth. Juveniles grew there and migrated to the innermost area of the bay, and then to the deeper areas as they grew. Growth of females showed a good approximation to a seasonally fluctuating von Bertalanffy equation, with a size-frequency distribution suggesting the presence of 2 or 3 cohorts per year. Body length of females attained 35–125 mm in the first winter and 105–150 mm in the second, and their life span is estimated to be about two years. Their reproductive season was mainly from June or July to September in the second year (ca. 1 year old), and mainly July in the third year (ca. 2 years old). The broad variation in the size range of reproducible females (BL 76–168 mm) suggests indeterminate growth. Males were smaller than females with overlapping cohorts but their life cycle appears to be similar to that of females.