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Fisheries Biologist:
Zeb Hogan

A Man on a 'Mega' Mission

Meet Zeb Hogan, a Ph.D. fisheries biologist who is heading up the National Geographic-funded 'Megafishes Project' - a three year project which aims to track and document the largest species of freshwater fish around the world. That's him in the photo at right, being dwarfed by the huge specimen of giant freshwater stingray he and his team discovered in Cambodia (this specimen was more than 13 ft/4m long).

He gets to travel around the world and explore rivers and lakes that are supposed to harbor enormous species of fish. In fact, scientists believe that the giant freshwater stingray may really be the largest species of freshwater fish in the world, reportedly growing up to 16.5 ft/5m long and weighing up to 1,320lbs/600kgs. This species was previously unknown to science until as recently as 1990. Dr. Zeb Hogan may very well get to be the lucky guy who discovers the world's largest specimen of stingray that beats out the current record holder - the giant Mekong catfish.

We spoke with Zeb Hogan and asked him a few questions about the kind of work he does.

ES: Are the really big fish also the oldest fish?

ZH: Fish have what's called 'indeterminate growth', meaning fish will keep growing larger as long they continue to live and are unchecked by disease. That means the larger fishes also tend to be the oldest ones.

ES: For most fish, you can tell the age of the fish by counting the rings on the scales. Large species of freshwater fish, like the giant Mekong catfish and the freshwater stingray, don't have any scales on their bodies. How can you tell how old these types of fish are when you catch a really big one?

ZH: We can use several methods besides examining scales to determine the age of a fish. For species without scales, like the catfish, we can examine the plates that cover the gills. We can also count rings on the otoliths [part of the inner ear] or even counts the rings on the vertebrae [the bones of the spine]. Unfortunately, to examine the otoliths or the vertebrae would involve sacrificing the fish, so we wouldn't use that method in the case of a fish we intend to return to the wild.

ES: The species that holds the current world record for largest freshwater fish is the Giant Mekong catfish. Are there any other contenders, or do you anticipate finding another specimen that could beat the current world record fish?

ZH: There are a couple of species that are close contenders. One is the giant freshwater stingray, which is believed to get much bigger than the Mekong catfish (over 1,300 lbs/600kgs). The other is a rarely seen fish called the Chinese paddlefish. Supposedly, they can grow up to 21 feet long, but there are no authenticated records of a paddlefish that size. These fish are extremely rare and endangered because the waters they inhabit [inland rivers in China, like the Yangtze River] have experienced an enormous amount of pollution, silting and overfishing. Chinese paddlefish are very rarely seen anymore, let alone enormous specimens.

A White Sturgeon was taken from the Columbia River in 1897 weighing 1,387 pounds. That's definitely bigger than the Giant Mekong catfish. But sturgeon aren't considered freshwater fish because they live out part of their lives in the ocean. One thing that Zeb Hogan and his team have discovered in their research on the Giant Mekong catfish is that that species also lives part of its life out at sea. One of the benefits of the research they are doing with the Megafishes Project is making important discoveries about the lifespan, range, habitat and breeding habits of these large fish. It may be that many of the largest species of "freshwater fish" in the world spend some or most of their lives living at sea and come into fresh water to spawn. The question becomes, "How do we determine if a fish is truly a freshwater species?" and "Do many of the species we assumed were exclusively freshwater, in fact, live part of their lives at sea?"

ES: At what point in your life/education did you decide to focus on large megafishes?

ZH: I was studying for my PhD and focused some of my research on the Giant Mekong catfish. I began to understand that many of the world’s largest inland freshwater lakes and rivers contained one or more species of giant 'megafishes' - freshwater fish criteria of over 6 feet and 200 pounds. I wanted to call attention to the endangered status of these magnificent fish. The Megfishes Project was funded by the National Geographic Society for the sole purpose of finding, documenting and studying these rapidly disappearing, incredible fish.

You can read more about the Megafishes Project and track the exciting finds of Dr. Zeb Hogan and his time by visiting the Megafishes website, or tracking the News dispatches on the National Geographic site dedicated to the Megafishes Project.