Why Are Fish So Slimy?

Why Are Fish So Slimy?

Nature and evolution have helped animals hunted by vicious predators and live in a dangerous environment to survive against all the odds. There are several reasons why a fish produces slime on its body. Nature has given fish this ability to protect themselves from predators, prevent infections from their open wounds, and prevent parasites from invading their bodies. 

Why Are Fish So Slimy?

There are several different reasons why a freshwater or saltwater fish would have slime on their body. It doesn’t mean that the surrounding water is contaminated or poisonous, or that the fish swam through slime. Many different creatures in nature produce slime, and each animal uses it for their own unique purposes. Without the ability to produce slime, many fish and other sea creatures who use it may have died out long ago. 

Reasons Why Fish Are Slimy

  • It is a defense mechanism.

The natural world is a violent place, and many creatures have developed different mechanisms to help them evade their natural predators and live another day. For many fish, they have developed the ability to produce slime on their bodies and fins to escape from the jaws of their worst enemy. The slime on their bodies assists them and helps them to escape. The slime makes the fish harder to grab onto, and they can swim faster through the water than if the fish only had their scales. But slime doesn’t just protect them from their predators in the waters they inhabit. It can also protect them from fishers who try to grab onto them and catch them as they wade in the water.

  • It contains poison.

Some fish have evolved so that their slime contains poison. This poison keeps predators from eating them. There are a few ways the poison slime could work. Some poison slime produces a foul odor that drives away their predators who smell the water to look for prey.

Another way that poison slime protects fish from death is when a large predator swallows them whole, the slime touches the inside of their mouth and causes severe irritation. When the predator fish realizes what is happening, it will spit them back up and no longer pursue them.

If a fish that produces poison slime reaches the inside of a predator’s stomach, the poison could severely irritate their stomach lining, and the predator will vomit them back up. 

  • It keeps them safe from parasites.

Parasites are creatures that do not hunt prey themselves. They attach themselves to an animal or fish, and they can either slowly kill their hosts from the inside or live in their mouths and eat whenever their host preys on and eats. But slime prevents certain parasites from attaching to a fish. If the slime is on a fish’s body, the parasite will not be able to latch onto the fish. 

  • Slime protects open wounds.

When a fish is injured in a fight with a predator or as a result of their environment, they will bleed out through their open wound. Like humans and other animals, fish are susceptible to developing infections and dying if they do not protect their open wounds. Humans invent antibiotics, dogs and cats lick their wounds clean, and many fish produce slime that prevents bacteria from infecting into their wound. Also, the slime coats the open wound in order to prevent the smell of blood from escaping and attracting more predators.

How the African Lungfish Survives in the Summertime

The African Lungfish uses slime in a specific way. During the summertime, when riverbeds and lakes dry up, the African Lungfish must find shelter so it can survive. So it will find an area inside of a lake or river that is still wet and then produces a lot of slime. Then the slime will harden around the lungfish’s body and create a cocoon. This is how the African Lungfish avoids death when the river or lake or its habitat dries up, and there’s no water left. These fish can survive in their cocoon for about one year. When the water returns to the area, usually during the rainy season, they will emerge from their cocoon and resume swimming. The lungfish also use their slime regularly to protect from the many parasites that live in their habitat. 

Where Does the Slime from their Bodies Come From?

Some fish produce slime as a bodily mechanism, and other fish can intentionally create slime. But when a fish produces slime, it comes from the cells of their skin that are underneath their scales. The fish’s body does not produce the slime itself, but a glycoprotein is released from the skin, and it mixes with the surrounding water that the fish lives in. When it mixes together, the slime then forms and coats the fish. 

Which Fish Produce Slime?

There are many different species of freshwater and saltwater fish that produce slime. Here are a few of the most common fish that produce slime:

  • Parrotfish
  • Asian catfish
  • Discus
  • Gourami
  • Betta fish
  • Snakeheads
  • Wrass
  • Sole fish
  • Tetra fish

But one of the most famous fish in the ocean that produce slime is called the hagfish. Their slime is so unique to anything else in the animal kingdom that scientists are studying it because they believe that their slime has many different properties that could advance industrial or medical materials. 


Fish developed the ability to produce slime because there are several advantages that a fish with slime has over fish that do not have slime. They’re able to easily slip away from predators and protect themselves from parasites by making their scales too slippery to attach themselves to their bodies or fins. Slime also acts as a living bandage if they’re wounded. It also protects against infections if the wound is large. Some slime contains poison, so if a predator comes after them, the slime will either cause the fish to taste bitter, stop pursuing them, or be a neurotoxin that stuns or kills their predator.

Continue reading: Why Do Fish Swim in Schools?

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