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Fish tale -- two pals vie for tiniest find
San Francisco Chronicle


February 06, 2006

A friendly international debate over the world's smallest fish has turned into a biology lesson on why it pays to be tiny.

Two ichthyologists - one in Seattle and the other in Switzerland - recently claimed in separate scientific publications to have discovered the smallest vertebrate animal ever known. And small they both are.

One, discovered by Maurice Kottelat, the Swiss biologist, in the acid water of an Indonesian peat swamp, is female and barely more than a third of an inch long, or smaller than the eraser at the end of a pencil.




But the other, found by Kottelat's longtime friend, Theodore W. Pietsch of the University of Washington, measures less than a quarter of an inch, or about the size of a well-worn eraser at the end of a pencil.

Unaware of Pietsch's fish, Kottelat reported his finding - a distant relative to carp and zebra fish - in the current online issue of Britain's Proceedings of the Royal Society, calling it "the world's smallest vertebrate." Its name is Paedocypris progenetica.

Meanwhile, Pietsch, reporting in the current quarterly issue of a journal called Ichthyological Research, described a curious little male anglerfish, found in the ocean more than 6,000 feet deep off the Pacific and Atlantic coasts of the United States.

Pietsch didn't actually go fishing for his tiny creatures, but studied samples of them borrowed from the collection at the Scripps Institution of Oceanography in San Diego. It was in that collection that he found the record-breaking small one, Photocorynus spiniceps.

The Swiss researcher quickly conceded that his little critter had lost out in the size competition.

"I've known Maurice for 25 years, and we're good friends," Pietsch said in an interview. "This is just a friendly rivalry, and we've been laughing together by e-mail since it began."

The two men agree that evolution has given major advantages to both fish species because of their miniature size. "Both fishes have evolutionary advantages that have adapted them for the worlds where they live," Pietsch said.

Pietsch's Photocorynus is a weird little thing. The male is actually a parasite, little more than a bundle of sperm that fuses for life to the female's much larger body - in most cases right near the vent from which she ejects her eggs, but occasionally on her back, Pietsch said.

"The females can live for 20 or 25 years, whether or not any males find them," he said. "But if the males can't find a female, they die, because it's the female who feeds them. So this is a wonderful way for a tiny male and a big female to get together and stay together, and when the male does fuse to a female, she can be reproducing all the time.

"Sometimes, in fact, the female will carry as many as eight small males, all attached to her, and she does all the swimming and eating for all of them."

Kottelat, the Swiss scientist, and his colleagues discovered his fish off the island of Sumatra and found that evolution has enabled that species to thrive in the dark, highly acidic, tea-colored water of rapidly vanishing teak swamps.

The females are the tiny ones in these fish, Kottelat said in an e-mail to The Chronicle. Their small size helps them survive whenever the swamps dry and only small shallow puddles remain, and of course they're so small that predators can't find them. The slightly larger males have extremely large pelvic girdles and fin muscles, which makes it easy for them to grasp the small females during copulation, or perhaps to move the eggs around after spawning, he said.

"Paedocypris progenetica is a complete fish which moves on its own, not just pulled by another fish, or pushed by the current," Kottelat said. "It lives in a complex habitat, chooses its microhabitat, predictably chooses its spawning site, maybe its partner, and certainly has a sophisticated courting and spawning behavior. It is a real miniaturized fish."

And as for who was first to find the world's smallest fish, Kottelat said: "We will keep the matter as entertainment for dinners during some ichthyology congress."


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