by Bob Thomas
If you’ve caught fish, you know they are very slimy. And virtually every species is, but why?
Slime in the result of glycol-proteins that are produced in the epidermis and combine with water to create mucus. Most have a thin layer, but some just gush slime, making them hard to hold and rather irritating to the squeamish.
One of the obvious functions of slime is that it reduces drag by coating the irregular surface of the scales, thus enabling the fish to slip easily through its environment.
But the slime also affords the fish protection against surface invaders like fungi, bacteria and ectoparasites, and it contains medicinal qualities that are soothing to open wounds. It is so effective that medical researchers are working feverishly to isolate the slime’s active ingredients in an attempt to find applications for human infections.
Another vitally important function of slime in fish is that it aids their balance of essential electrolytes by forming a two-way selective surface that maintains a livable osmoregulatory filter.
Fish exchange respiratory gases across their skin, and slime actually enhances the gas exchange efficiency across this surface.
Some fish slimes contain toxins that either immobilize their prey or give them protection from predators. There are species that are said to have such strong toxins in their slime that a shark bite is stalled in mid-chomp.
Some fish are known to use slime to create nests for their young, and others actually secrete copious amounts of protein-rich slime as food for their offspring.
In response to pending drought, African Lungfishes burrow into the soil and secret mega amounts of slime, resulting in the formation of a protective coating called a cocoon that allows them to survive until the rains reappear. Colorful Caribbean Parrotfish ensure their safety as they settle down in the evenings by secreting a slime balloon around their bodies that alert them to the approach of a potential predator.
Some fish eat their own slime, and some cultures use fish slime as an effective glue.
The next time you get slimed by a fish, don’t just gag and fuss. Enjoy the moment and consider slime’s value to its producer.