What Are the Causes of Brown Skin Spots on Goldfish?

By John Christopher

Keep a close eye on your goldfish. Injuries, disease and other ailments show up in a variety of shapes, sizes and colors. The sooner you notice problems, the sooner they can be remedied.


Woman examining large goldfish

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Check goldfish daily for bumps, spots, sores or other problems. A brown spot resembling a smudge or stain requires a different remedy than a brown bump. An early, accurate diagnosis improves your goldfish's chances of survival.


Girl looking at fish in tank

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Brown or black flat spots and patches on goldfish are a sign of ammonia burn from spiking ammonia levels. The discoloration is a sign of healing, but elevated ammonia levels can kill fish.

Small, distinct, raised brown or black spots or bumps are fish lice, a parasite that targets goldfish.


Cleaned fish tank with water changed

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For brown patches, change 20 percent of the aquarium water to cut down ammonia. Monitor levels with a test kit sold at pet centers and fish stores. Once ammonia levels drop, healing will continue and the dark patches should go away.

For brown or black dots, gently net the goldfish and remove it, holding it in a wet cloth--it can live a minute or two outside the tank. Use tweezers to remove the parasite, and treat the aquarium water with anti-parasite medicine available at pet centers. More than one treatment might be necessary.


Goldfish swimming together in tank

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Goldfish produce more waste than most fish do. Too many will quickly foul aquarium water, making them prone to ammonia burn. Do not overcrowd. Each goldfish should get 10 gallons of water.

Changing 20 percent of the tank's water twice a month helps maintain general health.


Goldfish swimming happily in tank

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Take care when using and storing goldfish medicines and treatments. Keep them out of the reach of children. Read the labels and follow all advice and precautions.

Never buy a sick goldfish hoping to cure it. It would probably die and take your other fish with it.