Catch of the day: Researcher stakes claim to tiny-fish title

By Sandi Doughton

Seattle Times staff reporter

UNIVERSITY OF WASHINGTON

This 1.8-inch female Photocorynus spiniceps has what looks like a small nub in the middle of her back. Actually, that's the male, the world's smallest known vertebrate.

Last week, scientists claimed this is the world's smallest known fish, discovered in Indonesia. The fish, a member of the carp family, has a translucent body and a head unprotected by a skeleton.

UW researcher Ted Pietsch shows a photo of the female Photocorynus spiniceps with the tiny male on her back. "He's actually fused to her body," said Pietsch, who has studied the creatures for 35 years. "He feeds off nutrients in her bloodstream."

Fishermen usually exaggerate the size of their catch, but biologists are engaged in a friendly feud over the title of the world's smallest fish.

An international team of fisheries scientists claimed the record last week with a type of carp that measures less than a third of an inch long and lives in Indonesian peat swamps.

Not so fast, says University of Washington researcher Ted Pietsch, who read a news article on the discovery last Thursday in The Seattle Times.

In his office, Pietsch has the only four specimens ever collected of a fish he says is "hugely smaller."

It's also a contender for strangest lifestyle.

Male anglerfish of the species Photocorynus spiniceps measure a scant quarter-inch long, which would make them not only the world's smallest fish but the smallest vertebrate, or animal with a backbone.

They spend most of their lives clamped onto females, which are many times larger. Biologists call the arrangement "sexual parasitism."

Though it sounds like something Dr. Phil would disapprove of, for anglerfish it's a matter of survival.

With their oversized heads and spiky bodies, the fish are adapted to the chill, dark waters up to a mile below the ocean surface. They get their name from the luminescent lure that dangles from their head and attracts prey. A vacuumlike swallowing action allows them to engulf meals as big as their own bodies.

At least that's how the females do it.

In species like spiniceps, males freeload.

"He's actually fused to her body," said Pietsch, who has studied the creatures for 35 years. "He feeds off nutrients in her bloodstream."

In their brief, free-swimming stage, the males rely on large eyes to spot the females' lures, and huge nostrils to sniff them out. Unable to feed on his own, a male who doesn't find a mate will die.

Some females — perhaps the Angelina Jolies of anglerfish — tote up to eight diminutive males on their bodies. But the fish are so rare that most females spend their entire 25- to 30-year life cycles traveling the depths without ever encountering a little Mr. Right, Pietsch said.

"The chance of finding each other down there is almost zero."

Scientists also have a hard time finding anglerfish. Occasionally, research ships snag one or two in their deep-sea trawl nets. Pietsch's spiniceps specimens were collected in the Philippines.

Pietsch published his description of the minuscule anglerfish in September and pointed it out last week in an e-mail to the scientists who thought their Indonesian carp was the world's smallest fish. Lead researcher Maurice Kottelat, of the National University of Singapore, graciously conceded the title.

"So our little fish is only the smallest freshwater vertebrate," he wrote in an e-mail. "Now I wait until the next smallest fish is discovered."

That might not take too long, said Christopher Kenaley, a UW graduate student who works with Pietsch.

About 200 new fish species are described each year, he said in an e-mail. And males of several anglerfish species still haven't been found.