What does Camallanus worms (Camallanus cotti) look like?

Red worms protruding from fish anus. Weight loss / sunken belly. Color fade.

How is Camallanus worms (Camallanus cotti) treated?

Levamisole HCl: Gold-standard treatment. Dose 2 mg/L (0.5 tsp per 10 gal of 10% solution). 3 doses 7 days apart. Treat the whole tank, not just visible-symptom fish.

FRESHWATER disease

Camallanus worms (Camallanus cotti)

Reviewed by the Fast Aquatics husbandry team · Updated May 2026

Quick referenceCamallanus cotti is a freshwater nematode parasite that protrudes from the fish anus as small red worms. Highly contagious between fish; treat the entire tank with Levamisole.

Symptoms

Red worms protruding from fish anus
Weight loss / sunken belly
Color fade
Lethargy
Refusing food
White stringy poop

Cause

Internal nematode parasite spread through infected fish, contaminated live food, or shared equipment. Common entry point: pet-store livebearers (especially mollies, guppies, platies).

Treatment options

Levamisole HCl. Gold-standard treatment. Dose 2 mg/L (0.5 tsp per 10 gal of 10% solution). 3 doses 7 days apart. Treat the whole tank, not just visible-symptom fish.
Fenbendazole (Panacur). Alternative or backup. Can damage shrimp + sensitive snails. 0.1g per 10 gallons, 3 doses weekly.
Manual removal. For visible worms - tweezers + isopropyl swab. Only catches what you can see. Always combine with chemical treatment.

Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology. Consult an aquatic veterinarian for valuable fish.

Prevention

Quarantine ALL new fish 30 days. Buy from breeder direct (avoid pet-store livebearers). Cull infected fish if treatment fails 2x.

Fatality + outcome

Moderate without treatment. Wasting + secondary infections kill the fish in 6-12 weeks. Treatment success rate: 90%+.

Full disease database · Symptom matcher · Q&A library · Glossary · QT timeline calculator

Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.