The Trang An Scenic Landscape Complex, a UNESCO World Heritage Site in Vietnam, is a biodiversity hotspot with exceptional ecological and cultural value. Despite its protected status, gaps remain in scientific knowledge, particularly regarding fish species diversity, water quality, and the impact of introduced species. In collaboration with Hanoi University of Education (HNUE), Three Monkeys Wildlife Conservancy (TMWC) conducted a comprehensive survey to address these gaps. The survey recorded 36 fish species from 31 genera, 16 families, and 8 orders, including three vulnerable species listed by the IUCN (Cyprinus carpio, Channa orientalis, and Oreochromis mossambicus). Additionally, three introduced species—Pterygoplichthys sp., Oreochromis mossambicus, and Gambusia affinis—were identified, raising concerns about their potential ecological impact. The survey also documented four marine or brackish-water goby species, underscoring the area’s rich and complex biodiversity. These findings provide baseline data crucial for informed conservation and management efforts, with the goal of protecting and sustaining the unique ecosystems within Trang An.