Causative agent: Camallanus spp. — parasitic nematode (roundworm)
Camallanus worms are a nightmare scenario for Australian livebearer enthusiasts — the sight of thin red worms protruding from a guppy's or molly's anus is both distressing and alarming. These nematode parasites live inside the intestines and hindgut of freshwater fish, and because the tiny larvae are passed in faeces and ingested by other fish or copepods, an infestation can silently spread through an entire guppy colony before any worms become visible. Infected fish gradually waste away, losing weight and appetite while their bellies become hollow. Treatment with levamisole is the most effective option available to Australian aquarium keepers and works by paralysing the adult worms, which are then expelled by the fish. Multiple treatment rounds spaced two to three weeks apart are essential to also address newly hatched larvae. All fish in the tank should be treated simultaneously even if symptoms are only visible in a few individuals, and the substrate should be thoroughly vacuumed to remove expelled worms and larvae.
Symptoms
- •Red-orange worm-like threads (1–2 cm) protruding from the fish's anus
- •wasting
- •hollow belly
- •loss of appetite
- •stringy or bloody faeces
- •lethargy
- •secondary infections
Treatment
- •Levamisole (most effective)
- •fenbendazole
- •flubendazole
- •treat entire tank
- •repeat treatment after 2–3 weeks to kill newly hatched larvae
Australian Medications
- •Levamisole via aquarium suppliers and some vets in Australia
- •Panacur (fenbendazole) via veterinary prescription
Commonly Affected Fish
- •All freshwater fish
- •livebearers (guppies, mollies, platys) and cichlids most commonly affected
Important Notes
Treat ALL fish in the tank, not just affected individuals. Multiple rounds required. Vacuum substrate thoroughly after treatment to remove expelled worms.