Changes in river systems, overfishing and the appearance of new, invasive species can lead to a drastic decline in the number of native fish inhabiting aquatic ecosystems. In the Ashida river basin in Japan, the bitterling fish (Rhodeus atremius suigensis), which was previously found in abundance, is now facing local extinction. This is concerning, considering that it is recognized as an indicator species for the conservation of fish diversity in freshwater ecosystems.
