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A fish's fins look ragged and frayed. What does Merck list this as a sign of?

A possible bacterial infection, often linked to poor water.

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  1. Ich or white spot disease
  2. Dropsy or pinecone disease
  3. A possible bacterial infection ✔

Why: Merck lists ragged fins among signs of bacterial infection, along with ulcers and swelling. Outbreaks are often tied to poor water quality and stress, so test the water too.

Huh, didn't know that: Merck says laboratory testing is needed to diagnose a bacterial infection and choose an effective antibiotic.

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Why was the fish so good at keeping its tank tidy? It had a lot of fin-esse.
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References

Answer: A possible bacterial infection. Merck lists ragged fins among signs of bacterial infection, along with ulcers and swelling. Outbreaks are often tied to poor water quality and stress, so test the water too.

  1. Merck Veterinary Manual: Disorders and Diseases of Fish www.merckvetmanual.com/all-other-pets/fish/disorders-and-diseases-of-fish
    ragged fins, or enlarged eyes. Diagnosis of a bacterial infection requires laboratory testing.
    Checked 2026-10-11.
  2. Merck Veterinary Manual: Bacterial Diseases of Fish www.merckvetmanual.com/exotic-and-laboratory-animals/aquarium-fish/bacterial-diseases-of-fish
    Predisposition to such outbreaks frequently is associated with poor water quality
    Checked 2026-10-11.
  3. Merck Veterinary Manual: Disorders and Diseases of Fish www.merckvetmanual.com/all-other-pets/fish/disorders-and-diseases-of-fish
    laboratory testing is necessary to determine which antibiotics will work
    Checked 2026-10-11.

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