Kangal, Turkey--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.