The pandalid shrimp Plesionika izumiae is a relatively common shrimp in the coastal waters of Japan, except off northern Honshu and Hokkaido. This is one of the dominant species in the benthic community of Kagoshima Bay, southern Japan. The reproductive biology including, reproductive period, size at sexual maturity, embryo size and brood size of P. izumiae was studied in the bay. All females were examined for the presence of embryos attached to the pleopods and the developing embryos were classified into four stages. Ovarian development was also observed based on morphological observation. Ovigerous females occurred throughout the year with higher percentage during May to November, indicating this was the main reproductive period. Ovarian maturation was observed during the incubation process of embryos, suggesting that females were potentially capable of multiple spawning during a reproductive period. The size at sexual maturity was estimated to be 8.5 mm in carapace length based on the method using the size at which 50% of the females were ovigerous. Embryo size was independent of the body size (carapace length) of females but increased with development. There was a positive correlation between brood size and body size, while a significant reduction of embryos was observed during the course of development.
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Vol. 31 • No. 3