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Why do fish and amphibians produce mucus on their skin?

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A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

In both fish and amphibians, the production of mucus is a vital function of the integumentary system. This slimy substance, formed by the combination of a protein called mucin and water, serves several essential biological purposes.1

Functions in Fish

In fish, mucous glands are particularly numerous, especially in teleosts and cyclostomes. The primary roles of this mucus include:2
* Locomotion: It lubricates the body, which lessens friction and aids in swimming.1
* Protection: It acts as a barrier against bacteria and provides physical protection for the body.2
* Osmotic Balance: It assists the fish in maintaining proper osmotic balance.2

Functions in Amphibians

Amphibians are characterized by their smooth, moist skin, which is maintained by numerous mucous glands located in the dermis. For these animals, mucus is critical for:34
* Respiration: Because many amphibians rely on cutaneous respiration (gas exchange through the skin), the mucus helps keep the skin surface moist, which is necessary for the diffusion of gases.56
* Environmental Interaction: It facilitates the diffusion of water and ions between the animal and its environment.6