The Murray cod can grow up to 6 feet long and weigh more than 250 pounds, and is rumored to eat everything from birds to snakes to possums even its own kind. But humans have been encroaching on the cod's river system, and now these enormous fish are rarely seen in the wild.

Each year in the Australian outback, the dry season leaves five top predators- giant stingrays, sawfish, bull sharks, and freshwater and saltwater crocodiles- stranded in waterholes with limited food supplies.

Researcher Zeb Hogan travels to Cambodia to find and study the little-known giant stingray.

Follow Dr. Zeb Hogan on his journey to find the largest freshwater fish in Australia: the freshwater sawfish.

Follow Zeb Hogan as he goes in search of the biggest and oldest of North America's river monsters: the White Sturgeon.

Follow Dr Zeb Hogan on his quest to find what could be the world's largest and most deadly freshwater fish: the giant freshwater stingray.

Aquatic ecologist Dr. Zeb Hogan teams up with kayaking experts to discover what monster fish are lurking beneath the surface in Rio Roosevelt.

They are carp from Asia which can jump 10 feet in the air at the sound of a boat motor, turning a day on the water into a boxing match.

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Dr Zeb Hogan travels to the American Midwest in search of the paddlefish, one of the largest, oldest and most bizarre -looking freshwater fish on the planet.

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Giant freshwater fish are studied at Khone Falls on the Mekong River in Laos.

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Zeb Hogan travels to Spain in search of the invasive Wels catfish -- a monster fish capable of growing more than 8 feet long, eating birds, cats, and, as some legends claim -- even humans! The voracious predator is not native to the region, and biologists fear it could be destroying the local ecosystem.

Flying fish from Asia are invading America's waterways and turning innocent boating trips into boxing matches as fish "knock out" anglers. National Geographic Explorer Zeb Hogan heads to the Illinois River, one of the areas where their population is thickest, to see what can be done to stop them ... and the answer could be as simple as your dinner plate.

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Dr Zeb Hogan searches the southern United States for the rapidly disappearing alligator gar.

Zeb travels Thailand in search of giant fish; freshwater protected areas.

Zeb Hogan is on a mission to find the giants of the sea.

Zeb travels to Spain for the wels catfish, a vicious predator that destroys local ecosystems.

Zeb Hogan attempts to fathom the uncontrolled spread of flying Asian carp in America's waterways.

Amazonian expedition to assess the impact of humanity on the area's fish population.