Camallanus Worms
Symptoms
Thin red worms (1-3 mm) protruding from the anus, often visible only intermittently as they retract. The worms anchor in the intestinal wall. Fish becomes thin despite eating, develops a bloated abdomen, loses color, and produces white stringy feces. Late-stage cases stop eating. Most common in livebearers (guppies, mollies, platies), Discus, and Apistogramma.
Causes
Nematode parasite transmitted by ingesting infected microcrustaceans (cyclops, daphnia) or from livebearer mother to fry. Often introduced through wild-caught fish, live foods from natural sources, or apparently-healthy carrier fish. Can lurk for months before symptoms appear.
Treatment
Levamisole hydrochloride is the standard treatment — paralyzes the worms so they release their grip and are expelled. Dose by package directions, with a follow-up dose 7-10 days later to catch worms that hatched after the first dose. Fenbendazole (Panacur) is an alternative. Treat the entire tank, not individuals — by the time one fish shows worms, the whole tank is exposed. Heavy gravel vacuuming during treatment removes expelled worms before they reinfect.
Prevention
Quarantine all new livebearers for at least 4 weeks. Treat suspected carriers prophylactically with levamisole even if asymptomatic. Avoid feeding wild-caught live cyclops or daphnia from sources you don't trust.
Notes
If you see red worms hanging from the anus, the infestation is already advanced — worms only show when the gut is overloaded. Treat immediately even if other fish appear healthy.