Researchers study world's largest freshwater fish

Scientists are studying a number of the world's largest species of freshwater fish to assess the conservation status of all species reaching over 2m in length or 100kg in weight.

According to a story from National Geographic News, the project, which is funded by the World Wildlife Fund (WWF) and National Geographic, will involve over 100 scientists in 17 different countries and aims to establish which species are in most need of conservation.

WWF conservation lead scientist Zeb Hogan told National Geographic: "This is the first study to examine all of the world's giant freshwater fish. Like previous studies of coral reefs and the deep sea, the study will serve as a window to an amazing underwater world that people seldom see."

National Geographic says that Hogan is currently collecting data in the Cambodian Mekong river system on Pangasius gigas (formerly Pangasianodon), which at over 300kg is regarded as the largest catfish in the world - as well as a contender for the world's biggest freshwater fish.

Pangasius gigas has suffered in recent years due to a combination of fishing, damming and the Upper Mekong Navigation Project.

The species is now protected and is listed on Appendix I of CITES, as well as in the current IUCN Redlist for fishes, where it is classed as critically endangered.

The Giant barb, Catlocarpio siamensis, which reaches 3m and 300kg is also vulnerable to fishing, Hogan says.

The team is also going to look at the Giant freshwater stingray, Himantura chaophraya, a species which was only described in 1990.

This ray, which is found in the Mekong and Chao Phraya basins, could grow larger than currently believed.

The National Geographic claims that there are some reports of this ray reaching over 500kg, which would make it the world's largest freshwater fish species if true.