It is one of the best-known relationships in nature: the anemone provides a tentacle-guarded home and the clown-fish drives off predators that would chew its protector. Recent research has, how-ever, shown there is much more going on. A study in 2009 revealed that waste excreted by clownfish provides vital nutrients to anemones. Now researchers have found clownfish can boost their hosts' oxygen supplies at night too. Clownfish and anemones live on coral reefs where oxygen levels in the water often plunge at night as photosyn-thesis shuts down. Some fish species are known to wave their fins over their coral homes in help keep the coral oxygenated, Joseph Szczebak of Auburn University, in Alabama, and his colleagues wondered if clownfish might do something similar for anemones.
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