Feeding off fish pee

I was really here to feed on your urea.  Image courtesy of University of Aberdeen.

I was really here to feed on your urea.

Image courtesy of University of Aberdeen.

Ammonia is toxic to aquatic animals and yet there is ample evidence that sharks and their kin are attracted to it. Many experts have argued that sharks use ammonia to track down their prey and, while that might be true, a new study is now revealing evidence that sharks are capable of converting the toxin into a valuable resource with their gills.

The new work began when a previous study noted that ammonia can be actively taken up by shark gills and transformed into urea. While interesting on its own, the finding led the biochemists behind the new research to question whether the sharks were getting something more out of this conversion. After working through the chemistry associated with the process, they speculated that sharks were obtaining a net nitrogen gain from the ammonia uptake. This was intriguing because nitrogen has to be obtained by sharks through meat. Moreover, it is required not only for them to grow but also for them to manage the salt in their blood. When the researchers monitored what sharks did with ammonia laced waters in the lab, they were stunned to discover that the predators use it to cover 31% of their daily nitrogen demands and can thus get by on considerably less meat. You can read more in The Economist article that I wrote on this here.