Pangasius conchophilus is one kind of catfish, this species distributes along Mekong River with large size, grown-up fast and high economic values, it has high demand in national and international markets, and this was added in the Red List of threatened species in 2012. Information about this species is very limited in Vietnam, appeared seasonal and distribution on the Hau River is unknown in both of size and quantitative aspects. The aims of study are to assess frequency and size of fish along the river, providing information to produce evidence database for development and protection the species in the Mekong Delta.

The study is carried out from 2012-2013 along Hau River, where is located in the Mekong Delta of Vietnam, the river is from An Giang (upstream) to Can Tho (midstream) and Soc Trang (downstream-estuarine). Trawl net was used to catch along the Hau River, the sampling was collected monthly by beam trawl net, mesh size of the net was 2a=2 cm, cod end was 1.5cm, the length beam was 3.5- 4 m. Results found length fish was 2-20 cm in the study, large fishes (>12 cm total length) appeared in upstream, midstream and downstream regions from July to October, whereas small fish (10 cm) were not found in this region. However, small fish is not significant different about frequency among upstream, midstream and downstream (p>0.05). Besides, Correlations of this species (size and quantity) with water quality (Chemical and physical parameters) are also discussed in the result.