Fish Get Sick Too

Have you ever seen a fish with something yucky growing on it? How about one swimming in circles? Fish, like all animals, get sick. Sometimes they get so sick they die. Most times, though, they get better and live.

What makes fish sick? Most of the same kinds of things that make you sick, make fish sick. There are four kinds of things that make fish sick.

Fish doctorFish

Viruses, bacteria

These very small critters can't be seen without a microscope. You get sick from a cold virus or germ, and fish get sick from them, too. They cause everything from skin diseases to "messing" up specific organs. They can attack a fish's kidneys or pancreas.



Ever seen a dead log in the woods? It has some white, hairy stuff growing on it­this is a fungus. It lives off the decaying log. The fungus gets important nutrients from the log. Fungus growing on fish does the same thing. Sometimes you will see fish with the white, hairy stuff growing from fins, gills, or even from the skin.


Other parasites

These small critters live on the outside or inside of the fish. They get nutrition from the fish. The fish also offers them a place to live. Biologists call the fish a "host." Critters, like worms and certain crustaceans, can attach themselves to the outside or inside of the fish.


Fish need lots of clean water to live. When certain chemicals get in the water, they get in the fish, too. Some chemicals "eat up" oxygen. Fish need oxygen to survive. When they don't get enough oxygen, they become stressed and might die. Some chemicals damage gills and other sensitive organs.

Why do fish get sick?

Fish swim with the things that make them sick. But why aren't they sick all the time? Sometimes fish are more sensitive to these things. That happens when the fish are stressed or weak. Spawning, migration, and long winters stress fish. Pollution and high and low water temperatures also stress fish. Stressed fish are prone to getting sick.

Can you eat sick fish?

Cooking fish kills the things that make fish sick. The things that make fish sick love cold-blooded critters. They don't like our bodies as much. This is why it is safe to eat fish that might be sick.

Sick Fish in the Hatchery

Fish in Commission hatcheries sometimes get sick. There they get medicine to make them healthy again. The Commission has a special "fish doctor" who diagnoses and treats diseases in fish. We want to make sure the fish we stock for you are healthy.

illustration-Ted Walke

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PLAY Summer 1999

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