Reproductive biology of the Japanese mantis shrimp Oratosquilla oratoria (Crustacea Stomatopoda): Annual cycle of gonadal development and copulation

We investigated the reproductive biology of the stomatopod Oratosquilla oratoria for both males and females of different size classes. Samples were collected from Tokyo Bay, Japan, by monthly bottom trawl surveys from May 2004 to October 2005. Histological examinations of testis, vas deferens, and penis for males and ovary and seminal receptacle for females were conducted. Males attained sexual maturity at a smaller body size (between 4 and 5 cm body length [BL]) than did females (BL > 7 cm). Although there were significant changes in the developmental stage of the testis between months, medium-to large-sized males (BL >= 7 cm) stored sperm in the vas deferens and penis throughout the year, indicating year-round functional maturity of the males. On the other hand, females showed clear seasonal patterns in ovarian maturation. Mature females were found between March and September. The early (May-June) and late (July-September) spawning peaks involved large (BL >= 10 cm) and medium (7 <= BL < 10 cm) size classes of females, respectively, confirming a similar trend shown by previous studies for size-related seasonal patterns in ovarian maturation. In addition, sperm was found in the seminal receptacle concurrent with ovarian maturation, suggesting that the timing of the onset of copulation is regulated by the sexual receptivity of females. This study is the first to reveal this size-related reproductive pattern in both sexes in the Stomatopoda.