Morphology of male reproductive organs of the rice field crab Esanthelphusa nani (Naiyanetr, 1984) (Brachyura, Gecarcinucidae)

Abstract

The rice field crab is considered a pest that disrupts rice production in paddy fields in tropical regions. The crab is also used as a stable food source by local people in many countries in Southeast Asia. For both of these roles, a good knowledge of the crab’s reproductive biology is necessary to manage populations in their natural habitats. This study aims to investigate the reproductive cycle of adult males of the rice field crab Esanthelphusa nani (Naiyanetr, 1984). Males crabs were sampled monthly in a paddy field; individuals were then anaesthetized and dissected, and their reproductive tract was analysed. The gonadosomatic index (GSI) was evaluated based on the relative weight of the reproductive tract and body weight. The male GSI showed significant temporal difference, with the highest levels in June, August and September. Based on GSI and macroscopic examination, the testis and vas deferens can be classified into three stages of increasing size: (1) resting stage, (2) developing stage and (3) active stage. Microscopic examination revealed that the testis and vas deferens had a tubular structure. Seminiferous tubules in the testis underwent spermatogenesis and spermiogenesis at every stage. The vas deferens consisted of three major regions: anterior, middle and posterior, which showed different types of epithelia. Interestingly, the microscopic structure of the vas deferens was similar among these three reproductive stages. It is also important to note that round-shaped spermatozoa were found in different parts of the reproductive tract, including the seminiferous tubule and vas deferens, as well as in the female seminal receptacle, whereas no spermatophores were found in this species. Overall, this study shows that mature sperms can be found in the reproductive tract of male E. nani throughout the year, indicating that males have prolonged spermatogenic activities. The rice field crab is considered a pest that disrupts rice production in paddy fields in tropical regions. The crab is also used as a stable food source by local people in many countries in Southeast Asia. For both of these roles, a good knowledge of the crab’s reproductive biology is necessary to manage populations in their natural habitats. This study aims to investigate the reproductive cycle of adult males of the rice field crab Esanthelphusa nani (Naiyanetr, 1984). Males crabs were sampled monthly in a paddy field; individuals were then anaesthetized and dissected, and their reproductive tract was analysed. The gonadosomatic index (GSI) was evaluated based on the relative weight of the reproductive tract and body weight. The male GSI showed significant temporal difference, with the highest levels in June, August and September. Based on GSI and macroscopic examination, the testis and vas deferens can be classified into three stages of increasing size: (1) resting stage, (2) developing stage and (3) active stage. Microscopic examination revealed that the testis and vas deferens had a tubular structure. Seminiferous tubules in the testis underwent spermatogenesis and spermiogenesis at every stage. The vas deferens consisted of three major regions: anterior, middle and posterior, which showed different types of epithelia. Interestingly, the microscopic structure of the vas deferens was similar among these three reproductive stages. It is also important to note that round-shaped spermatozoa were found in different parts of the reproductive tract, including the seminiferous tubule and vas deferens, as well as in the female seminal receptacle, whereas no spermatophores were found in this species. Overall, this study shows that mature sperms can be found in the reproductive tract of male E. nani throughout the year, indicating that males have prolonged spermatogenic activities.