Adjusting to A New Home

Diversion of water for agriculture from a lake in Western China, compounded by climate change, is leading to a decline in water level during the past fifty years. The naked carp that feed and grow in the increasingly saline water have adapted by drastically changing their physiology.

Endangered naked carp migrate annually between freshwater rivers, where they spawn, and Lake Qinghai, where they feed and grow. However, the is drying up and becoming increasingly more saline--leading to surprising adjustments to the carps' metabolic rate.

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.

Naked carp respond to the increased salinity of the lake water 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, 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," explained the researchers.

Long-term lake-water-acclimated fish also adjust by actively feeding and have much larger fat stores, the researchers found. In contrast, migrating river fish are anorexic, relying on protein breakdown and higher oxygen consumption to generate energy.

"If the lake continues to dehydrate, these benefits may change to pathology," the researchers said.

---LiveScience Staff

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Credit: Chris Wood