New research conducted by the University Of Queensland has found that the Round Headed Parrotfish’s night time cocoon of mucous is actually to protect the fish from parasite attack. Previously it was thought the mucous ‘sleeping bag’ was to mask the scent of the fish from predators.
Parrotfish on The Great Barrier Reef Australia are preyed on by gnathiids which are 2 mm long parasitic isopods. They can suck blood from the unfortunate parrotfish and can carry a blood disease similar to malaria.
According to this research the Round Headed Parrotfish makes a “mosquito net” of mucous filled with gelatine to protect itself from attack at night!
More information here.