Fritz Expel-P — Levamisole HCl Nematode Treatment
Fritz Expel-P — Levamisole HCl Nematode Treatment
Active ingredient: Levamisole HCl (nicotinic acetylcholine receptor agonist / anthelmintic)
Levamisole acts as an agonist at nicotinic acetylcholine receptors (nAChR) in nematode muscle tissue. Nematode nAChRs are far more sensitive to levamisole than vertebrate receptors — the drug causes sustained spastic paralysis of parasitic worms, which are then expelled from the fish's gastrointestinal tract. Paralyzed worms do not die immediately; they are expelled alive and must be physically removed from the tank to prevent ammonia spikes as they decompose.
Target Parasites
| Parasite | Common Name | Presentation |
|---|---|---|
| Camallanus cotti | Camallanus worm | Orange or red hair-like threads protruding from the vent — most visible at night or under stress; most common nematode in hobby livebearers (guppies, mollies, platies) |
| Camallanus lacustris | Camallanus worm | Same presentation; frequently affects angelfish, discus, and cichlids |
| Capillaria spp. | Threadworm / hairworm | White stringy feces, hollow belly, wasting; common in discus and fish kept in planted tanks |
| General intestinal nematodes | Roundworms | Declining body condition despite feeding, stringy feces, progressive emaciation |
What Expel-P Does NOT Treat
- Nematode eggs — levamisole does not kill eggs; a mandatory second treatment in 3–4 weeks is required to eliminate newly hatched larvae before they mature
- Flukes (monogenean trematodes) — no activity against Dactylogyrus or Gyrodactylus
- Protozoan parasites — no effect on ich, velvet, Hexamita, or Spironucleus
- Bacterial or fungal infections — no activity against these
Critical Post-Treatment Step
Perform a large water change (50%+) 24–48 hours after dosing and siphon the substrate thoroughly. This physically removes expelled and paralyzed worms from the tank before they decompose. Decomposing worm biomass will spike ammonia — this is especially dangerous in heavily stocked or small tanks and can cause secondary losses if not addressed.
Treatment Protocol
- Remove activated carbon before dosing
- Dose per label directions; can be mixed into food for fish that are reluctant to feed normally
- Perform a large water change with substrate vacuuming 24–48 hours after treatment
- Retreat in 3–4 weeks to eliminate larvae that hatched from eggs that survived the initial dose — skipping this step virtually guarantees reinfestation
Plant Safety
Some aquatic plant species are sensitive to levamisole. If treating a heavily planted display tank, test in a separate container with a plant cutting before committing to a full tank dose. If invertebrate-safe deworming in a planted tank is the goal, consider Fritz Expel-F (flubendazole) instead.
Invertebrate Safety
Generally considered safe for shrimp and snails at recommended doses due to differences in vertebrate and invertebrate nAChR subunit composition. As a precaution, remove shrimp to a separate container during treatment if the tank population is high value.
Expert guidance
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Cameron draws on 25+ years in the hobby and a marine biology background to help you choose the right fit for your system.