Nematode Biology and Parasitism

Camallanus cotti and related species are formidable, blood-feeding nematode parasites that aggressively infect the lower intestines and rectum of freshwater teleosts, particularly livebearers (Poeciliidae), cichlids, and anabantoids. Unlike many parasitic nematodes, Camallanus features a direct or facultative indirect life cycle. Viviparous females expel fully formed, free-living, first-stage larvae ($L_1$) directly into the water column. These larvae can be ingested by intermediate hosts (copepods or crustacean larvae) or ingested directly by a susceptible fish. Upon ingestion, the larvae molt and migrate to the intestine, where they utilize a heavily sclerotized, jaw-like buccal capsule to anchor deep into the mucosal lining, feeding continuously on the host's blood.

Clinical Identification

• Anal Protrusion: The definitive diagnostic sign: small, thread-like, reddish-brown worms protruding from the anal vent, particularly when the fish is stationary. The red coloration is derived directly from the host's hemoglobin.
• Abdominal Distension or Wasting: Depending on the worm burden and secondary bacterial infections, the abdomen may appear highly distended or severely emaciated.
• Scoliosis: Severe curvature of the spine resulting from nutritional depletion and muscle atrophy.
• Chronic Lethargy: Anemia resulting from the relentless blood feeding causes profound weakness.

Transmission Vectors

1. Live Foods: Introduction via contaminated cyclops, Daphnia, or other crustacean intermediate hosts.
2. Infected Livestock: Asymptomatic carriers introduced without proper quarantine protocols.
3. Direct Ingestion: Larvae ($L_1$) persisting in the substrate and water column ingested directly during bottom foraging.

Anthelmintic Chemotherapy

The eradication of Camallanus requires potent paralyzing or metabolic-inhibiting anthelmintics.

• Levamisole Hydrochloride: The pharmaceutical of choice. Levamisole acts as a nicotinic acetylcholine receptor agonist, causing spastic paralysis of the nematode's musculature. The paralyzed worms lose their grip on the intestinal wall and are expelled. Standard dosage is 2 mg/L in the water column for 24 hours, followed by a massive water change. Treatment must be repeated after 2 and 4 weeks to eliminate newly hatched larvae.
• Fenbendazole: An alternative benzimidazole anthelmintic that disrupts tubulin polymerization. Administered via medicated food at a 1% concentration for 3-5 consecutive days.
• Gravel Vacuuming: Vigorous daily substrate siphoning is critical to remove expelled worms and free-living $L_1$ larvae.

Prophylactic Husbandry

• Strict Quarantine: Prophylactic administration of levamisole to all new fish in a bare-bottom quarantine setup.
• Avoidance of Wild Live Food: Refrain from feeding wild-caught copepods or unsterilized aquatic invertebrates.