What Does a Fish Use Mucus For?

Disease

• All fish with a slime coat use it to protect themselves from parasites. The slime coat acts as a second skin, an extra barrier between the fish and viruses, bacteria, protists, fungus and parasites. Parrotfish take this to another level, producing an actual cocoon of slime when they sleep. Researchers have discovered that these mucus cocoons block roughly 90 percent of parasites while the parrotfish remain relatively immobile during sleep.

Deterring Predators

• Some fish actually use their slime coats to deter predators. The hagfish, a primitive jawless fish, will release thick, unpalatable mucus when threatened. This mucus makes the hagfish very slippery and hard to catch, but also makes it less tasty to predators. The slime cocoons of parrotfish double as a deterrent to predators. This strategy is often quite effective, since very few predators enjoy biting through a shroud of mucus if there's any alternative prey available.

Feeding Young

• Some fish use their slime coats to feed their young. Among fish, parental care is not common, let alone producing food for the offspring. However, the discus fish̵2;and, some suspect, the related freshwater angelfish̵2;provides a meal to its young by producing more mucus to feed them. The parental strategy of producing food for the young with the body is almost never seen outside of mammals.

Problems with the Slime Coat

• In the home aquarium, several factors can cause problems with your fishes' slime coats. Stress from poor or incorrect water chemistry can cause a fish to stop producing skin mucus, and physical damage from fights or handling can scrape off the mucus. This leaves a fish more vulnerable to disease. However, you can replace a fish's slime coat with an artificial one. Products available at aquarium shops are designed to be added to aquarium water to coat fish with a protective slime until they can make their own. Often these products also include dechlorinators and other water conditioners.