In Search of the World's Biggest Fish

Hogan and collaborators with a giant freshwater stingray, in Thailand. PHOTO COURTESY OF ZEB HOGAN

For more than a decade, researcher Zeb Hogan has spent much of his time traveling around the world on a singular mission: to find and learn more about the world's largest freshwater fish. Through his photographs and a show he hosts on Nat Geo Wild called "Monster Fish," he's helped many people discover and appreciate these beasts.

The highlights of his research on the conservation status and accurate size of various fish are being presented beginning March 25 at the National Geographic Museum in Washington, D.C., an exhibition Hogan describes as a "one-stop-shop for everything megafish."

His main finding: Most of these fish are now threatened with extinction due to habitat degradation, dam building, pollution and over-harvesting.

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Hogan and others with a nearly 8-foot-long Mekong giant catfish, in November 2007. Photo courtesy of Zeb Hogan

Throughout the course of his work, Hogan has seen some fascinating beasts. He has laid eyes on the two contenders for the world's largest freshwater fish. Officially, that title goes to the Mekong giant catfish; fishermen in northern Thailand caught a huge specimen of the catfish that weighed 646 pounds and was 9 feet long, on May 1, 2005. "But a lot of people, myself included, think that giant freshwater stingrays may be larger," says Hogan, a researcher at the University of Nevada, Reno. (Largetooth sawfish, which are found in fresh and saltwater, get even bigger, reaching weights of 1,300 pounds and growing to 23 feet in length.)

The Southeast Asian giant stingray (Himantura polylepis) can grow to 8 feet wide and over 15 feet long. The largest specimens found in the past few years haven't been weighed, because that procedure can kill them, and they are endangered. Then there's the animal's Australian cousin, Himantura dalyensis, which can rival the Asian species in size. A similar variety found in Paraguay called the short-tailed river ray (Potamotrygon brachyura) grows to "at least 600 pounds, possibly much larger," Hogan says.

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Hogan with a goonch. Photo courtesy of Zeb Hogan

There are misperceptions about some of these megafish. Some have alleged that goonches, a type of catfish found in South and Southeast Asia, have eaten people, he says. In reality these fish are generally more afraid of humans than we are of them, and this species is in "urgent need of protection," Hogan says.

Swimming with these fish can be unnerving, though, he says. While many fish are skittish, some are quite curious. Arapaima, an Amazonian fish that can reach up to 10 feet in length, "will come right up to you to investigate," he says. A large fish called barramundi will do the same thing, with an added twist: They can tell where you are looking and tend to approach via your blind spot—so you turn around and find yourself face-to-face with a huge undersea animal, he says.

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Hogan with a giant Siamese carp. Photo courtesy of Zeb Hogan

Olaf Jensen, fish ecologist at Rutgers University, says that the exhibit is "great stuff. Zeb has done a fantastic job of bringing the conservation challenges regarding big fish to a public audience." Jensen has collaborated with Hogan to study the world's largest trout, known as a the taimen, in Mongolia. They have found that these species require large stretches of river to survive, and that there is a growing number of people catching and releasing the animal.

These fishermen must buy permits from the government, money which goes to conservation efforts. While overfishing can harm animals, and has in the past in many areas, well-regulated catch-and-release fishing can be beneficial, since it can help prevent development and damming of river areas, Jensen adds. It's common practice to require fishermen to buy permits, to provide funds for conservation and wildlife management, he says.

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Hogan and others with a white sturgeon in British Columbia's Fraser River. PHOTO COURTESY OF ZEB HOGAN

Others in the research community have lauded Hogan's efforts to spread the word about big fish.

"Zeb has been [at] the forefront of trying to bring attention to this particular group of fishes and their conservation needs," says Donald Stewart, a researcher at the State University of New York in Syracuse. "Through his involvement in the [Monster Fish] series as well as his own field studies, he has significantly broadened the general public's knowledge of and appreciation for these amazing animals."

Relative size of different fish. Courtesy of Zeb Hogan