New Trap May Take Deep-Sea Fish Safely Out of the Dark

John Roach
for National Geographic News
July 1, 2004
In the cold and dark depths of the seas, some fish attract their prey with bioluminescent lures. Others have huge mouths that allow them to chomp enough food in a single bite to sustain them for weeks.

Scientists are eager to learn more about these creatures, but whenever they try to bring them up to the surface and transport them to a laboratory, they die.

"You can only learn so much from studying dead things, and it gets really frustrating," said Jeffrey Drazen, a marine biologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California.

The fish die from the tremendous and sudden changes in temperature and pressure. Many of these species live at depths of several kilometers, where temperatures are slightly above freezing and the pressure is of several hundred atmospheres. At sea level, air pressure is equal to one atmosphere, or about 15 pounds per square inch (7 kilograms per every 7 square centimeters).

As the fish are brought to the surface, their bodies, which are adapted to cold, dark, high-pressure environments, cannot cope.

For example, said Edward Seidel, enzymes, which are essential for functions such as digesting food, have specific shapes that allow them to function under the extreme pressure of the deep sea. Seidel is a curator at the Monterey Bay Aquarium in California.

"When you release that pressure, the shape of the enzyme changes, and since it changes, it no longer functions and the animal no longer can survive," he said.

To remedy the problem, Drazen has designed a high-pressure fish trap. The trap should allow him to capture fish at the bottom of the ocean and bring them up to the surface at the same pressure and temperature that exists in their native home.

"From there you could perform a variety of controlled experiments on them and do all those things intertidal marine biologists have been doing for decades, but that we have not been able to do," he said.

Drazen is keeping details of the trap under wraps until he and his colleagues publish the first of their scientific results in a peer-reviewed journal. He anticipates this sometime early next year.

Trap Applications

According to Drazen, there are several applications for the high-pressure trap. His specific interests lie in the metabolism of the deep-sea animals as compared to their surface dwelling cousins. He is also intrigued by their pressure tolerance.

"When we yank up species they undergo large pressure changes and usually they don't do well," he said. "But what would happen if we slowly acclimated them to lower pressures, what would their capacity be?"

Other scientists are interested in studying things like how sensitive these animals' eyes are to light and what sort of other stimuli they respond to.

"Of course, if we actually manage to acclimate fish to atmospheric pressure, then the side benefit will be that some of the strange, bizarre-looking animals could be on display," Drazen said.

Aquarium Display

The potential to acclimate deep-sea fish to atmospheric pressure is particularly exciting to Seidel. If successful, deep-sea fish could be displayed in the aquarium's exhibit on Monterey Canyon, a more than 10,000-foot-deep (3,000-meter-deep) canyon in the Pacific Ocean near Monterey.

The exhibit opened in the late 1990s, and more than 60 different species are on display, but none of them come from water deeper than 3,280 feet (1,000 meters).

Seidel would like to display fish such as the rattail, a species that he says is the "real ambassador" of the deep sea. The fish can survive at depths up to 19,700 feet (6,000 meters) and have large heads and mouths with long, tapering tails. Some species weigh up to 18 pounds (8 kilograms) and can grow 6 feet (1.8 meters) long.

"We also know they are very sensitive to pressure," Seidel said. "We think that with a trap like Jeff's we'll be able to capture an animal and slowly, over the course of days or weeks, acclimate it to one atmosphere pressure and then, potentially, be able to display it."

The aquarium has also done some research and development on pressurized tanks to display fish, but a window on such a system has to be so small that only one or two people can look into a tank at a time.

So, will Drazen's trap be a success? Will deep-sea researchers successfully acclimate a rattail to atmospheric pressure?

"These animals are like Martians. They live in an environment so different from where we live," Seidel said. "We are just starting to understand what it takes to keep these animals alive. We are doing pioneering work. It's hard to say if we'll be successful or not."

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