Fish mucous cocoons: The 'mosquito nets' of the sea

Alexandra S. Grutter, Jennifer G. Rumney, Tane Sinclair-Taylor, Peter Waldie, Craig E. Franklin

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Mucus performs numerous protective functions in vertebrates, and in fishesmay defend themagainst harmful organisms, although often the evidence is contradictory. The function of the mucous cocoons that many parrotfishes and wrasses sleep in, while long used as a classical example of antipredator behaviour, remains unresolved. Ectoparasitic gnathiid isopods (Gnathiidae), which feed on the blood of fish, are removed by cleaner fish during the day; however, it is unclear how parrotfish and wrasse avoid gnathiid attacks at night. To test the novel hypothesis that mucous cocoons protect against gnathiids, we exposed the coral reef parrotfish Chlorurus sordidus (Scaridae) with and without cocoons to gnathiids overnight and measured the energetic content of cocoons. Fish without mucous cocoons were attacked more by gnathiids than fish with cocoons. The energetic content of mucous cocoons was estimated as 2.5 per cent of the fish's daily energy budget fish. Therefore, mucous cocoons protected against attacks by gnathiids, acting like mosquito nets in humans, a function of cocoons and an efficient physiological adaptation for preventing parasite infestation that is not used by any other animal.

Original languageEnglish (US)
Pages (from-to)292-294
Number of pages3
JournalBiology Letters
Issue number2
StatePublished - Apr 23 2011
Externally publishedYes


  • Behaviour
  • Coral reefs
  • Gnathiidae
  • Mucus
  • Parasites
  • Scaridae

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • General Agricultural and Biological Sciences


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