Galapagos Catch Yields New Species

The hydrothermal vent fish that scientists captured near the Galapagos Islands this year has several characteristics distinguishing it as a new species never described before, two California scientists have concluded.

“This one is particularly different because it has more fin rays, those bony elements that support the fins. It’s got more vertebrae. And then the eyes are further apart,” said Daniel M. Cohen of the Los Angeles County Museum of Natural History.

He and Richard H. Rosenblatt of Scripps Institution of Oceanography are collaborating on the identification.

The fish, captured with a robotic arm attached to the research submersible Alvin, belongs to the genus Bythites. Until the Pacific fish was netted, there had been only three known species in that group, all dredged up accidentally in the northern Atlantic.

Informally, the new Bythites goes by “pink vent fish,” to distinguish it from the only other fish captured at vents where geothermally heated water is spewing out of cracks in the ocean floor. About a foot long, the pink vent fish is shaped like a tadpole and has unusually large gills.

A whitish vent fish, christened Thermarces cerberus by Cohen and Rosenblatt, was first captured accidentally by the Alvin in 1981. Since then, eager scientists saw the other vent fish many times through the Alvin’s thick windows, but they had a long wait to collect one.

They strung baited and unbaited hooks off the side of the submersible and farther out. They set traps. They even tried to poison it. But the fish wasn’t interested.

So excitement was high when Scripps scientists aboard the Atlantis II radioed that Alvin had captured the fish with a net, during a two-month Galapagos expedition that ended in May.

“Oh, my gosh, I’ve been trying to get one for 10 years,” Cohen said, his voice rising with glee even months after the fact. “Exciting is hardly the word for it. My wife could hardly get me to shut up.”

Customs Let Fish Go

The one hitch in Cohen’s plans to scrutinize the fish as quickly as possible came when Alvin’s mother ship, the Atlantis II, was impounded by U.S. Customs inspectors in San Diego because of a minute amount of marijuana found on board. Fevered negotiations with the government finally got the scientific cargo, including the fish, cut loose.

All the fuss about the vent fish comes because scientists want to know more about a chain of life discovered only within the past decade. Instead of an energy cycle based on sunlight and photosynthesis, they rely on poisonous hydrogen sulfide gas emitted by the vents as their source for life.

Chemosynthetic bacteria are known to live inside giant tube worms and clams around the vents, oxidizing the hydrogen sulfide into a usable energy form. But what feeds the vent fish, which have been seen nuzzling into the poisonous warm water above the vents?

Cohen said he could find little to answer that question in the fish’s visible structure.

“Some of the biologists who studied the vent area have theorized that these fishes live on bacteria that grow in the sulfur-laden water. Their theory is that it’s straining them out or gobbling up mats of bacteria,” Cohen said. But the gills aren’t designed that way, he said.

“I can tell by looking at the gills that it doesn’t strain. It doesn’t have a straining apparatus. But the gills are long, so it must use them for something.”

The biochemists, too, have found no clues yet, said George N. Somero, professor at Scripps who is heading an analysis of tissue taken from the fish.

He suggested that, like crabs around vents, the fish may survive the poisonous gas by converting hydrogen sulfide to a nontoxic chemical called thiosulfate. Then, they could survive by eating bacteria or smaller fish, he said.

Somero’s lab will analyze enzyme levels in the tissue to determine whether the fish has a higher metabolism level than other deep-sea fish--an indication of relying on the vents for energy. It also will look at the fish’s protein molecules, to see whether the relatively high water temperatures around vents result in structures that are more stable than those seen in fish from colder waters.

After the descriptive analyses are complete, the fish will get locked into a special cabinet in a hallway at Scripps’ Ritter Hall. There, it will be available to others who want to study it, as well as serve as a reminder of scientific fallibility for Cohen.

“I had predicted it would be in a different genus,” Cohen said with a grin. “So you see, a fish in the hand is worth a lot more than a fish through the window.”