Problems of biological invasions in the fish fauna of southern Vietnam: the example of the Dong Nai River basin

Abstract

Biological invasions of fish are among the key drivers of transformation in freshwater ecosystems, particularly in regions with intensive aquaculture development and high anthropogenic pressure. The aim of this study was to assess the extent of introduction and degree of naturalization of non-native fish species in the Dong Nai River basin (southern Vietnam), as well as to identify patterns of their spatial distribution and main pathways of introduction. Ichthyological sampling was conducted in April–May 2025 at 56 stations in the upper and middle reaches of the Dong Nai River, including the Da Nhim and Da Dang rivers, their tributaries, and lentic water bodies in Dong Nai and Lam Dong provinces. A total of 17 non-native fish species were recorded across 13 of the 17 surveyed areas. The highest diversity of introduced species was observed in large water bodies subjected to significant anthropogenic impact, particularly in Tri An Lake (11 species), as well as in the middle reaches of the Da Nhim River and the Dai Ninh Reservoir (6 species each). In contrast, the number of non-native species was considerably lower in highland areas of the Central Highlands (1–3 species), while no alien species were recorded in water bodies within Cat Tien National Park. Most species exhibited low to moderate occurrence frequency; however, two species—guppy (Poecilia reticulata Peters, 1859) and Nile tilapia (Oreochromis niloticus (Linnaeus, 1758))—showed very high prevalence. The results indicate a substantial scale of biological invasions in the Dong Nai River basin. Aquaculture and the aquarium trade are identified as the primary sources of non-native fish introductions, while their spatial distribution is strongly associated with the level of anthropogenic impact and the type of water body.