Zeb Hogan is a fish biologist who conducted research on the Colorado River while studying for his bachelor's degree at the University of Arizona, but now he's exploring rivers all around the world.

Hogan is a researcher and assistant professor at the University of Nevada in Reno, but he's also the host of "Monster Fish"on National Geographic.

The one-hour show has focused on more than two dozen of the planet's most amazing aquatic inhabitants.

“My primary research focus is the ecology and conservation of giant freshwater fish. So, these are fish that grow to over six feet long or weigh more than 200 pounds," Hogan said during a recent visit to Tucson.

Hogan said, similarly to other wildlife around the world, giant fish are facing common threats including pressure from burgeoning human populations, water pollution, and the construction of dams in their habitats.

Hogan said he hopes measures are taken now to save some of these special species- for some, he said, it is probably too late.

Hogan recently visited Tucson to attend the 25th anniversary of the UA Undergraduate Biology Research Program, where he participated while attending school here.