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Which fungus does Merck link to grayish-white, cotton-like growths on fish?
A fungus called Saprolegnia.
- A fungus called Saprolegnia ✔
- A normal slime coat
- Leftover food stuck on
Why: Merck says Saprolegnia causes grayish-white, cotton-like growths on the skin, gills, eyes or fins. Columnaris bacteria can also look cotton-like, so a fuzzy appearance alone does not prove the cause.
Huh, didn't know that: Merck says columnaris, a bacterial disease, can also cause slimy or cotton-like sores.
Why did the mushroom get invited to every party? Because he's a fungi.
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References
Answer: A fungus called Saprolegnia. Merck says Saprolegnia causes grayish-white, cotton-like growths on the skin, gills, eyes or fins. Columnaris bacteria can also look cotton-like, so a fuzzy appearance alone does not prove the cause.
- Merck Veterinary Manual: Disorders and Diseases of Fish www.merckvetmanual.com/all-other-pets/fish/disorders-and-diseases-of-fish
Signs include grayish-white, cotton-like growths on the skin, gills, eyes, or fins.
Checked 2026-10-11. - Merck Veterinary Manual: Disorders and Diseases of Fish www.merckvetmanual.com/all-other-pets/fish/disorders-and-diseases-of-fish
This fungus can spread to the internal organs and deeper tissues of the body.
Checked 2026-10-11. - Merck Veterinary Manual: Disorders and Diseases of Fish www.merckvetmanual.com/all-other-pets/fish/disorders-and-diseases-of-fish
Signs may include skin lesions with slimy or cotton-like excretions.
Checked 2026-10-11.
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