The freshwater prawn genus Macrobrachium has more than 270 known species, with remarkably high species diversity in tropical freshwaters. Most of the widely distributed species in the Pacific have amphidromous migratory life history, which allows them to expand their range via ocean currents.
In this study, Yusuke Fuke, JSPS Postdoctoral Fellow at the National Institute of Genetics, and Tomoaki Maruyama of Trend Design Co., Ltd. identified the specimens collected from Miyako Island as Macrobrachium mammillodactylus (Thallwitz, 1891) based on genetic and morphological analysis. This marks the first record of this species in Japan and its northernmost distribution. This species has been previously reported from Australia to central Taiwan. The specimens collected in this study were adults, suggesting that they likely overwintered on the island, indicating an expansion of their range to the Ryukyu Archipelago.
Range expansion from Southeast Asia to the Ryukyu Archipelago and Honshu has been observed in other southern freshwater shrimp species. By accumulating fundamental range data, we may be able to identify and predict the factors contributing to the range expansion of amphidromous species.
Figure: Macrobrachium mammillodactylus collected from Miyako Island, Japan. Photo by T. Maruyama.
