Channels between lakes and rivers play a crucial role in maintaining fish population dynamics and their diversity in floodplains. In order to better understand the spatial distribution and the biomass of fish in the channel connecting the Lake Poyang and the Yangtze River, a mobile hydroacoustic survey was conducted in September 2014, using Simrad EY60 split-beam echo sounder (200 kHz).The spatial distribution of fish density and biomass for each cell of the studied region was derived from the spatial interpolation with geostatistics of ArcGIS. The results showed that the mean target strength (TS) in the investigated areas is -56.4±6.4 dB and the mean total length is about 7.6 cm, ranging from 1.2 to 98.0 cm. Average fish density in the channel was 53.7 ind./1000 m³, ranging from 0-441.7 ind./1000 m³. Horizontally, fish assemblages were unevenly distributed in the investigated areas and concentrated mainly in three areas, that is, the section near Hukou Country, Xieshan and Pingfeng Hill, respectively. The most striking feature in fish density was the concave-shaped distribution in the channel along the water flow direction (from lake to river).The fish size (total length) in the area near Lake Poyang (Area Ⅲ) was significantly smaller than that in the waters near Yangtze River (Area Ⅰ) and the transition zones (Area Ⅱ). One possible reason for this might be a large number of young-of-the-year fish emerged after spawning period. Fish density increased vertically from the upper layer of the water to the lower layers. Meanwhile, our results supported the generality of the phenomenon of increasing fish size with increasing depth (i.e., bigger-deeper phenomenon). In addition, the total amount of fish biomass in the investigated area was estimated to be 6.2×10⁷ ind., up to 620 tons. Our findings suggested the need to enhance the protection for these essential fish habitats. This study also contributes to the knowledge of the current state of fish resources and can be useful for proper resources conservation and effective ecosystem management of the floodplain biodiversity.