Fish are a group of animals that are aquatic and have gills to breath oxygen from the water. They come in many different shapes, sizes and varieties and can be found in both fresh and salt water. Fish are cold-blooded and have no digits. Most fish use large fins and a specially shaped tail to navigate through the water. There are approximately 32,000 species of fish around the world.
Why are Fish Slimy?
The majority of fish can be described as being slimy to the touch. Fish secrete a glyco-protein from cells located in the outside layer of the skin. When the glycol-protein comes in contact with water it creates a slimy mucous coating. The primary reason that the fish excretes this mucous is to protect itself from harmful parasites and bacteria. The slimy coat contains enzymes and antibodies that fight off viruses, bacteria and other pathogens before they can enter the body of the fish. When a fish is injured or sustains a cut the slime protects the open wound from becoming infected.
The slimy coating also stops the fish losing important electrolytes and body fluids. It makes it difficult for these to pass from the fish into the surrounding water. A tiny breach in the slime coating can allow this to happen due to osmosis. Fish exchange oxygen with the water through their skin also and the slime coating helps to regulate that reaction.
The slime coating also helps protect the fish from predators. Many fish secrete a toxin along with the glyco-protein. When eaten this may discourage other attacks on the fish. The slime can also be used to form protective cocoons.
Another reason for the slime covering is to make the fish more streamlined to help it swim faster. Some fish produce slime that can feed their young. This is often high in proteins and fats, which helps the young to develop quickly.