mucus

The slipperiness of a fish arises largely from the fact that 'single-celled glands in [its] epidermis' produce a fibrous secretion, which 'swells up in water to form a thick layer of viscous mucus'. This mucus has a range of different functions - protecting the animal from 'infections and parasites', lessening 'the danger of damage to the skin through collisions', allowing the fish 'to escape the grasp of predators', 'seal[ing] the body' to prevent the exchange of ions and water', and 'reduc[ing] frictional drag during locomotion'. (All these quotations come from John J. Videler's book, Fish Swimming.)

The parrot-fish even wears a 'nightgown' of mucus, a kind of transparent 'garment' which it takes half an hour to produce, starting at its mouth and incorporating a flap at either end. The New Scientist in January 1960 reported that the fish 'spins the nightgown while leaning against coral or hiding inside conch shells' and added '[e]xperiments have proved that the gelatinous feel of the garment discourages the appetite of the moray eel.' On waking up, the parrot-fish swims away and leaves the garment behind it in the water.

Some fish produce no mucus. Others produce vast quantities of it, the hagfish, for example, which generates the stuff in prodigious quantities:















To be slimy is to be strange ... but to be slippery is useful. (Turkish wrestlers cover themselves with oil to make it more difficult for their opponents.) I need to produce some psychological mucus to stop people getting hold of me...