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May 26, 2007

Human Flesh-Eating 'Doctor Fish' — Episode 3: 'It's like meat for them'


So said Fevzi Bardakci, a biologist at Turkey's Adnan Menderes University, quoted in Matt Mossman's article in the latest (June 2007) Scientific American.

Episode 1 on December 16, 2006 focused on Japan while more recently, on May 15, 2007, Episode 2 took us to China.

Now we learn that it all began in Kangal, Turkey.

Here's Mossman's story.

    Fish That Go Skin-Deep

    Trapped fish adapt to a life of nibbling on humans

    Tucked between brown hills in central Turkey is a natural hot spring where, for a fee, you can become fish food. Dip in a hand or foot, and within seconds small fish will swarm, bump and nibble it. Stand above the pools, and the fish will gather below, waiting. The scaly swimmers — the "Doctor Fish of Kangal" — supposedly have curative powers. But in this unusual case of adaptive ecology, the human visitors may be helping the fish more than themselves.

    These fish have acquired a taste for humans largely because they have little choice. The spring is too hot to sustain enough algae and plankton to feed them all. In the past, the fish were able to move between the spring and a creek that runs nearby. But after learning of a story about a local shepherd whose wounded leg healed after being dipped into the spring in 1917, builders walled off the spring from the creek in the 1950s to preserve a captive school. A Turkish family has now constructed a hotel, villas and a playground and markets the resort to psoriasis patients. Some 3,000 people every year pay for the privilege of sitting in the spring and allowing these omnivores to eat their dead skin, a process that may stimulate new skin growth or relax patients and thereby ease stress-triggered psoriasis.

    Unquestionably for the fish, "the human skin is a big help," remarks Fevci Bardakci, a biologist at Turkey's Adnan Menderes University. "It's like meat for them." In 2000 Bardakci published a paper in the World Wide Web Journal of Biology on Garra rufa, one of the two species found in the hot spring. He discovered that memebers of the same species that swim in a nearby creek grow to an average 97 millimeters and about 11 grams. In the hot spring, the fish are three-quarters the length and weigh one quarter as much. Moreover, during the summer spawning season, the trapped females grow fewer and smaller oocytes, the cells that develop into eggs. In the creek, the gonads balloon from 3 percent of body weight to almost 8 percent. In the hot spring, organs increase from 1 percent of body weight to 2 percent. They would grow even less without submerged skin to nibble, Bardakci concluded. Some 90 percent of visitors arrive in the summer, providing a nutritional supplement at the perfect time.

    The fish come from the carp and minnow family, which is known for adaptability, says Richard Londraville, a biologist at the University of Akron. He adds that those in the hot spring may eventually evolve into a separate species in a few thousand years.

    Other fish survive in waters as hot as or hotter than this spring, which hovers near 34 degrees Celsius. None are widely known to feed on skin, which may explain G. rufa are catching on elsewhere. A Chinese spa-building company, which claims to have invented the concept, says on its Web site that it trained its own doctor fish and built 10 spas in China, including in Beijing. Some of the Turkish fish were scooped up and enlisted in springs in Japan, where at several spas they are now also performing fish pedicures.

May 26, 2007 at 10:01 AM | Permalink


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