Influence of the domestic alien fish Rhynchocypris oxycephalus invasion on the distribution of the closely related native fish R. lagowskii in the Tama River Basin, Japan

摘要

In Japan, domestic freshwater fish are accidentally introduced into non-native freshwater habitats by human activity, such as the planting of fish. Introduction of the domestic alien fish may have a detrimental effect on native fish inhabitants. However, investigations on the distribution and establishment of such domestic alien fish in non-native river basins and their influence on native fish remains limited. Therefore, we investigated the distribution and establishment of the domestic alien fish Rhynchocypris oxycephalus and its influence on native fish in the Tama River Basin, Japan. Specifically, we used mitochondrial DNA and morphological analyses to clarify the influence of the invasion of this species on the distribution of the closely related fish R. lagowskii, which is native to the river basin. Fish sampled from the upstream section of the main river were mostly R. oxycephalus. This indicates that R. oxycephalus has replaced R. lagowskii in the upstream region. Fish sampled from the downstream section of the main river were mostly R. lagowskii. R. oxycephalus was also captured from agricultural canals linked to the Tama River, and in streams connected to the river via the canals. These observations indicate that the agricultural canal water networks facilitate the invasion of R. oxycephalus to peripheral habitats, such as canals and streams. In contrast, R. lagowskii was found in streams that flowed into the upstream section of the Tama River, with these streams having many large drop structures, indicating that drop structures prevent R. oxycephalus from invading aquatic habitats in these streams.