AMMONIA is as repulsive to most marine animals as it is to land-lubbing ones—and for good reason. It is extremely toxic. But there is an exception. Far from being repelled by ammonia, sharks are actually attracted to it. The longtime assumption has been that this is because it is a waste product, voided into the water by fish and other creatures, that signals the presence of potential prey. But Chris Wood and Marina Giacomin of the University of British Columbia, in Vancouver, think there may be more to it than this. As they describe in the Journal of Experimental Biology, they suspect that for sharks, ammonia is itself a useful resource.
All animals make ammonia. It is a compound of nitrogen and hydrogen produced by the breakdown of amino acids, the building blocks of proteins. Marine creatures can flush it directly into the sea (fish do so through their gills), since it is soluble in water. Land animals often add carbon and oxygen to convert it into urea, which is far less toxic, and store the result in solution in a bladder, for periodic evacuation. Sea creatures can make...Continue reading
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