internal parasite
Camallanus worms (nematode)
Thin, reddish-brown worms visibly protruding from the fish's vent (anal opening). Camallanus are internal roundworms that embed in the gut lining. One of the few internal parasites visible to the naked eye. Highly contagious within a tank all fish must be treated, not just visibly affected individuals.
Do first
- Confirm visually look for 0.5–2 cm reddish-brown worms protruding from the vent.
- Treat ALL fish in the tank, not just the ones showing worms others will be infected without showing symptoms.
- Do not attempt to pull the worms out manually. This can tear the gut lining and is lethal.
- Quarantine this tank's equipment Camallanus spreads easily between tanks.
- Stop feeding live foods (tubifex, bloodworm) if these were being used, as they can transmit Camallanus.
Escalate if
- Fish declining rapidly despite treatment heavy worm burden may have caused irreversible gut damage.
- Mass protrusion of many worms from multiple fish severe outbreak requiring aggressive treatment.
- No improvement after two correct treatment rounds.
Water clues
These readings can push this pattern higher or lower in the triage result.
ammonia above zero+1
Poor water quality weakens fish and may accelerate Camallanus progression correct water quality anyway.
Care protocol
Follow only the steps that fit your species, tank inhabitants, and medication label.
Confirming Camallanus
- Observe the fish from the side near the vent area. Worms protrude during rest and when the fish is mildly stressed.
- Worms are reddish-brown, thin (< 1 mm), and 0.5–2 cm in length.
- They may retract when the fish is disturbed. Watch for a few minutes.
- Multiple fish showing wasting and stringy feces without visible worms likely also have Camallanus. The worm burden may be lower or the worms may not protrude constantly.
Cautions
- Do not confuse with feces or intestinal prolapse.
- Do not try to remove the worms physically. It is almost always fatal.
Treatment protocol
- Treat with fenbendazole (Panacur/Safe-Guard), the most commonly used and effective option. Dose in food at 0.25% by dry weight for 3 consecutive days.
- Alternatively, use levamisole as a bath treatment. Follow species-specific dosing instructions carefully.
- Treat all fish in the tank at the same time.
- A second treatment round 3–4 weeks later is strongly recommended to catch newly hatched larvae.
- After treatment, perform large water changes and vacuum substrate to remove dead worms and larvae.
- Disinfect the tank if fully breaking it down. Larvae can survive for weeks in substrate.
Cautions
- Fenbendazole can harm some invertebrates. Remove snails and shrimp if treating the display tank.
- Dead, dying worms inside the fish can cause a local inflammatory reaction. Monitor closely after treatment.
- Levamisole can be toxic if overdosed. Measure carefully.
- Do not skip the second treatment round. Incomplete treatment leads to recurrence.
Source notes
References and context notes used for this triage entry.