The non-native freshwater fishes of Hong Kong: diversity, distributions, and origins

Non-native fishes are widespread in Hong Kong and many are likely to be established. Extensive field surveys, literature reviews, and citizen science data were used to determine the diversity, geographic distribution, potential introduction sources, and known impacts of non-native freshwater fishes in Hong Kong. In total, 95 species, including five putative hybrids, were recorded. In comparison, there are 65 species of native freshwater fishes. The majority (62 species) of non-native fishes belonged to five families: Cichlidae (27 species), Cyprinidae (15 species), Poeciliidae (eight species), Xenocyprididae (eight species), and Channidae (four species). Half of all non-native species had at least one breeding population. Potential introduction sources were grouped broadly into three categories: aquarium trade (associated with 62 species and two hybrids); aquaculture (20 species and three hybrids); and water transfers from mainland China (13 species). Most of the species recorded are native to Central and South America (27 species), East Asia (21 species), Southeast Asia (15 species), or Africa (15 species). However, a lack of experimental or manipulative studies and a scarcity of historical data limits our understanding of the extent of their ecological impacts. This synthesis of all currently available information could provide a basis for future research work and policy/management strategies that seek to pre-emptively reduce the likelihood of further species introductions to minimise potential harm to the environment.