Quirks and Quarks

Sharks recycle toxic ammonia to keep their skin moist

A shark species has a novel recycling technique that helps it survive
Spiny dogfish shark (NOAA/CBMNS)

The Pacific spiny dogfish shark is small as sharks go, but big when it comes to recycling.  A new study by Dr. Chris Wood, a zoologist from the University of British Columbia, has found that this shark can absorb toxic ammonia through its gills and turn it into useful urea. Urea is a nitrogen-containing substance that the shark stores in its blood.  By doing so, the shark is able to retain fluid, which prevents the skin from drying out in saltwater conditions. 

Researchers estimate that this recycling process also enables the shark to extract from the ammonia about 30 percent of the nitrogen it needs to survive.  This enables the dogfish shark - and possibly other sharks - to go for long periods without food.   

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