Thuong, N.V. (2008). Classification of the Pangasianodon hypophthalmus in the Mekong River. Scientific Journal of Can Tho University, Specific Issue on Aquaculture and Fisheries 2008(1): 84-89. (Full paper in Vietnamese).
Pangasianodon hypopthalmus (Tra catfish) are characterized by a laterally compressed body, a short dorsal with one or two spines, a well developed adipose, a long anal fin, strong pectoral spines, and two pairs of barbels (maxillary and mandibulary). The position of the mouth is decribed as being terminal. There are 6 branched dorsal fin rays and the pelvic fins have 8-9 soft rays. The gill rakers are described as being normally developed, with small gill rakers being interspersed with larger ones.Pangasianondon hypophthalmus have the swimbladder with a single chamber extending posteriorly above anal fin.
The natural range of Pangasianodon hypophthalmus is limited to the lower Mekong Basin, includes Cambodia, Lao PDR, Thailand and Viet Nam, and the Chao Praya River in Thailand.
Over their native range, Tra catfish are divided into two distinct populations: stocks in the Mekong River in Cambodia and Viet Nam belong to one population (southern stock); and stocks above Khone Falls in Lao PDR and Thailand form a separate population (northern stock). The southern stock is subject to more intensive fishing than the northern stock, and is larger in size.