Naked carp take seven to ten years to reach reproductive size. Although historically abundant, overfishing and destruction of spawning habitat through dam-building caused the species to become endangered during the 1990s. Diversion of water for agriculture from the lake has been compounded by climate change, leading to a decline in water level in the lake of 10?2 cm per year during the past fifty years (see accompanying image).
However, Chris M. Wood (McMaster University) and coauthors found that naked carp respond to the increased salinity of the lake water in a surprising way--by taking a "metabolic holiday." In the first forty-eight hours after transitioning from the freshwater river system to lake water, the carps' oxygen consumption falls --eventually reaching just 60 percent of that in river fish.
Both gill and kidney functions also decline. The sodium/potassium pump (Na+/K+-ATPase), which is a protein critical for cellular function, operated at only 30 percent of its capacity in lake-water fish compared to river-water fish. Ammonia-N secretion by the kidneys declines by a surprising 70 percent, and urine flow decreases drastically to less than 5 percent of its rate in the freshwater river water.
"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," explain the researchers.
Long-term lake-water-acclimated fish a
Source:University of Chicago Press Journals