India, Sept. 14 -- T he Mekong giant catfish is a toothless bottom-feeder. This is not the admonition it sounds like. The iconic species can live to the age of 60, grow to 10 ft long and weigh up to 300 kg. As for the bottom-feeder detail, they play a vital role in keeping the river and riverbed healthy, by munching on algae and detritus. For a giant, the species is rather elusive, though. It is known to swim hundreds of km along the Mekong River, between its feeding and spawning sites, but is rarely sighted. All this makes tracking, monitoring and conservation difficult. Meanwhile, dams and overfishing are altering its massive riverine ecosystems, causing its numbers to plummet. Mekong giant catfish were once found all along the 4,900-km l...