Mekong
Natural history

The Mekong basin is one of the richest areas of biodiversity in the world. Only the Amazon boasts a higher level of bio-diversity. Biota estimates for the Greater Mekong Subregion (GMS) include 20,000 plant species, 430 mammals, 1,200 birds, 800 reptiles and amphibians, and an estimated 850 freshwater fish species (excluding euryhaline species mainly found in salt or brackish water, as well as introduced species). The most species rich orders among the freshwater fish in the river basin are cypriniforms (377 species) and catfish (92 species).

New species are regularly described from the Mekong. In 2009, 145 species previously unknown to science were described from the region, including 29 fish species, two bird species, 10 reptiles, five mammals, 96 plants, and six amphibians. Between 1997 and 2015, an average of two new species per week were discovered in the region. The Mekong Region contains 16 WWF Global 200 ecoregions, the greatest concentration of ecoregions in mainland Asia.

No other river is home to so many species of very large fish. The biggest include three species of Probarbus barbs, which can grow up to 1.5 m (5 ft) and weigh 70 kg (150 lb), the giant freshwater stingray (Himantura polylepis, syn. H. chaophraya), which can reach at least 5 m (16 ft) in length and 1.9 m (6 ft 3 in) in width, the giant pangasius (Pangasius sanitwongsei), giant barb (Catlocarpio siamensis) and the endemic Mekong giant catfish (Pangasianodon gigas). The last three can grow up to about 3 m (10 ft) in length and weigh 300 kg (660 lb). All of these have declined drastically because of dams, flood control, and overfishing.

One species of freshwater dolphin, the Irrawaddy dolphin (Orcaella brevirostris), was once common in the whole of the lower Mekong but is now very rare, with only 85 individuals remaining.

Among other wetland mammals that have been living in and around the river are the smooth-coated otter (Lutra perspicillata) and fishing cat (Prionailurus viverrinus).

The endangered Siamese crocodile (Crocodylus siamensis) occurs in small isolated pockets within the northern Cambodian and Laotian portions of the Mekong River. The saltwater crocodile (Crocodylus porosus) once ranged from the Mekong Delta up the river into Tonle Sap and beyond but is now extinct in the river, along with being extinct in all of Vietnam and possibly even Cambodia.
keywords:forbidden_words, detectable_content:postscript