A Faculty for Fish

Guillermo Orti seated in office holding fish
April 25, 2011

By Rachel Muir

A few years ago, Guillermo Orti spent 10 days on an expedition in a remote region of the Brazilian Amazon. Along with his colleagues, he netted about 4,000 fish.

It’s part of his quest to better understand the evolution of the piranha and its myriad species.

Last August, Dr. Orti again headed to the Amazon, this time on an expedition organized and filmed by National Geographic. A show featuring the expedition airs May 3 on the National Geographic Channel and focuses on the “Megapiranha,” a creature that existed millions of years ago.

The show was inspired by a recent fossil discovery in Argentina. “Researchers found a piece of jaw bone with three teeth that was an intermediate form between piranhas and pacus, a related South American fish,” explained Dr. Orti, who is the Louis Weintraub associate professor of biology at GW. From the size of the bone, researchers estimate the fish was four or five feet long, more than twice as long as piranhas today.

To answer questions about what the prehistoric fish ate and why it became extinct, National Geographic researchers are trying to reconstruct the life of the Megapiranha. “The only way you can do it is look at the living species and extrapolate from there,” said Dr. Orti, who was interviewed multiple times for the show over the course of the expedition.

“National Geographic wanted to make a show about this in part because piranhas have a reputation of being ferocious, carnivorous and dangerous,” said Dr. Orti.

So how accurate is that reputation?

“It’s mostly fantasy,” said Dr. Orti. Rather than feasting on human flesh, piranhas typically “nibble” pieces of other fish, including their fins or scales. “Although they certainly have razor-sharp teeth and a powerful bite, they’re mainly scavengers so if anything dies and falls into the water, it will be eaten up,” he said. “But piranhas are not dangerous to humans. We are in the waters where piranhas live all the time when we’re on expedition.”

He said piranhas’ notoriety got a boost from an account by Teddy Roosevelt, who after a 1914 trip to Brazil described the fish as the “embodiment of evil ferocity” that would “snap a finger off a hand incautiously trailed in the water.”

“Who knows what Roosevelt actually saw but it helped spark the legend,” said Dr. Orti, “and a popular perception is hard to change.”

Dr. Orti researches the evolution of piranhas and other fish by examining the structure of their DNA molecules, a field called molecular systematics. “We compare DNA molecules among organisms and based on those comparisons try to reconstruct their family tree,” he said.

His expeditions in South America—piranhas only live east of the Andes in the continent—involve collecting and dissecting thousands of fish.

“We know there are a lot of species that haven’t yet been described in this region,” he said. “We’re collecting everything we can put our hands on.” It’s estimated there are about 80 species of piranha, but the expeditions also collect hundreds of other types of fish.

“We’re either on a boat moving from place to place or we’re fishing with all kinds of gear, including nets, lines and hooks,” he said. The researchers cut off a piece of tissue from each fish and preserve it for DNA analysis, while the bodies go into big barrels full of formaldehyde, which are later given to museums.

On the expeditions, it’s hot and buggy. “You smell like fish no matter what,” Dr. Orti said. Instead of piranhas, the real risk comes from stingrays, which can deliver an incredibly painful sting if stepped on, he said.

The thousands of specimens collected on the expeditions provide years’ worth of research, said Dr. Orti, who works with graduate students in his Lisner Hall lab to analyze and compare samples. His National Science Foundation-funded research to assemble the tree of life for fish involves a multi-institutional collaboration to decipher the evolutionary relationships among all groups of fish.

Fish have been a longtime fascination for Dr. Orti, who began working with the national fishery agency in his native Argentina while in college and became interested in the evolution of piranhas and their relatives in graduate school.

And for him piranhas aren’t just a research subject. They’re also a tasty treat.

“Bony but good,” he said. “Fish are my favorite food.”

Learning & Research

A Faculty for Fish