The scientists studied endangered naked carp that migrate annually between freshwater rivers, where they spawn, and a lake in Western China, where they feed and grow. However, Lake Qinghai is becoming increasing dry and saline.
Chris Wood of McMaster University and colleagues discovered the carp respond to the increased salinity by taking a "metabolic holiday." Forty-eight hours after transitioning, the carps' oxygen consumption falls, eventually reaching just 60 percent of that in river fish -- and both gill and kidney functions also decline.
"In other words, the kidney changed from an organ which excreted water at a greater rate than salt in river-water, to one which conserved water relative to salt in lake-water," explained the researchers.
"The (oxygen consumption) data indicate the cost of living for the naked carp is 40 percent lower in lake-water than in river-water, and that this difference is almost complete within 12 hours after transfer," said the researchers. "The magnitude of this response is remarkable."
The study will appear in the January/February issue of Physiological and Biochemical Zoology.