It is well known that parrotfish and some wrasse species produce a night time sleeping bag from mucus but until recently there was no evidence to really support the assumptions and theories. Most nature books and references have echoed the common belief that the mucus cocoon protects the sleeping fish by masking it’s smell from predators like moray eels and sharks. The hypothesis was mostly true because the cocoon appears to be particularly effective at protecting the wearer from nocturnally active parasites like biting isopods, the mosquitoes of the sea.
By bedding large parrotfish in isolated tanks, researchers were then able to experimentally manipulate the presence or absence of mucus cocoons at night and they added plenty of biting isopods to all the test tanks to test how the mucus cocoon would work as a deterrent. Sure enough, parrotfish with intact cocoons had much fewer bites from isopods than those that did not. It is not yet known whether the cocoon is a chemical or a physical barrier to isopod bites, perhaps it’s a combination of both, but it sure would be nice to get ‘Parrotfish Mucus Cocoon’ in a bottle to prevent reef fish against our common parasites, even if it was specific to wrasses. Sleeping parrotfish photo by FlickR user Syngnathidae.
[via Wired Science]