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How do fish defend against sickness? © Getty Images

How do fish defend against sickness?

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Ah choo! Nemo is sick and tired of getting colds, thankfully fish have an immune system that can protect against illness.

Asked by: Rachel Morris, Leicester


Most fish have an immune system similar to other animals with backbones. They produce antibodies that detect and bind to substances invading the body, like viruses and bacteria, and instruct white blood cells to destroy them.

Just like in humans, it’s possible to vaccinate a fish against future infections by exposing them to a less virulent strain of a disease-causing microbe. Fish also cover themselves in a layer of sticky mucus that traps microbes and contains antimicrobial chemicals. The more stressed a fish gets, the more infection-fighting goo it makes.


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Dr Helen Scales is a marine biologist, broadcaster and science writer. She is the author of Spirals in Time and The Brilliant Abyss.


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