fish

Fish Lice (Argulus)

A parasitic crustacean that attaches to fish, causing visible disc-shaped parasites, scratching, and blood spots. Common in ponds. Treatment: manual removal + potassium permanganate.

Symptoms

Disc-shaped parasites (2–5 mm) attached to the body, fins, or gills, sometimes visible as moving specks.
Scratching, flashing, and red blood spots where lice attach (E1).
Lethargy and appetite loss in heavier infestations.

Common Causes

Argulus crustacean parasites introduced with new fish, especially pond-raised stock (E1: common in ponds).
The parasite completes its life cycle freely in pond conditions.
Stress and crowding increase vulnerability to attachment damage.

What to Check

Inspect the body and gill covers closely for flat disc-shaped parasites.
Check any recent pond-fish additions — they are the usual source.
Plan both manual removal of adults and a water treatment for free-swimming stages (E1: manual removal + potassium permanganate).

What Not to Do

Do not rely on manual removal alone — larvae remain in the water and re-attach.
Do not apply pond-strength potassium permanganate doses to a small aquarium.

This guide is informational and does not replace professional veterinary advice. If fish are severely ill, consult a veterinarian.

Fish Lice (Argulus)

Symptoms

Common Causes

What to Check

What Not to Do

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Fish Lice (Argulus)

Symptoms

Common Causes

What to Check

What Not to Do