River Catfish

The river catfish may be overshadowed by its famed cousin, the Mekong giant catfish, which shares the same river system in Southeast Asia. But this less celebrated species is a remarkable fish in its own right and, at 5 feet (1.5 meters) and 99 pounds (45 kilograms), it has no apologies to make in the size department.

River catfish are known to inhabit Tonle Sap Lake in Cambodia. Every year they leave the lake and enter the Mekong River as part of their annual spawning cycle. Breeding begins at the onset of the region's rainy season (May-July).

These unique fish have the nickname "iridescent shark catfish," a seemingly ill-suited comparison for a toothless, freshwater fish. The nickname arises from its tendency to swim close to the surface, raising its dorsal fin above the water. As for iridescence, river catfish have no scales, but their delicate skin is covered with a protective layer of slime that gives them a shiny glow.

These fish are threatened with habitat fragmentation, industrial pollution, and overfishing. Many millions of people depend on the Mekong River for sustenance, and river catfish have long been targeted for their succulent meat.

They are extensively farmed along some sections of the river, such as in Thailand, where wild specimens have become quite rare.

National Geographic Emerging Explorer Zeb Hogan is attempting to learn more about these catfish by conducting a large-scale tagging and monitoring study. Since 2004, his team has tagged more than 3,000 river catfish in hopes of documenting their behavior and helping authorities to provide better protections.