Biochemical characteristics and antibiotic properties of the mucous envelope of the queen parrotfish

Abstract

Many species of wrasse (Labridae) and parrotfish (Scaridae) produce mucous cocoons at the beginning of each night. The mucus envelope which covers certain species of parrotfish throughout the night was first described by Winn (1955). The functional morphology of the slime producing gland has been investigated by Casimir (1971) and Lenke (1991). Large globlet cells in a folded epithelium form the opercular gland in the gill cavity under the operculum. The fish remain motionless inside the cocoon throughout the night. It is believed to be an antipredator device (Shephard, 1994). Parrotfish dash out of the mucous envelope when it is touched (J. J. Videler & G. J. Geertjes, pers. obs.) suggesting a function as an early warning system. A masking eVect for olfactory and tactile stimuli that could attract foraging common spotted moray eels Gymnothorax moringa (Cuvier) has been suggested (Winn & Bardach, 1956). It could also protect the fish from parasite settlement and the possibility of antibiotic properties has been predicted by Lenke (1991). Note that none of the functions mentioned are mutually exclusive. Whatever the function may be, it would require the cocoon to remain intact throughout the night at temperatures close to 30)C. A bactericidal eVect of the envelope could protect not only the cocoon but also the fish. Fish skin mucus has been targetted as a potential source in the search for novel antibiotics. It contains specific immunoglobulins, agglutins, lectins and lysins, especially lysozyme (Shephard, 1994). Antibacterial ion channel forming proteins from carp