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, which is why Fritz has you repeat the treatment one week later to catch larvae as they hatch
- 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
Fritz's direction is a 25% water change after 24 hours, taking care to remove the excreted worms and parasites. Siphon the substrate while you do it. This physically removes expelled and paralyzed worms before they decompose — decomposing worm biomass will spike ammonia, which 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: 1 packet per 10 gallons (38 L). Can be mixed into food for fish that are reluctant to feed normally
- Perform a 25% water change with substrate vacuuming 24 hours after treatment, removing the excreted worms
- Repeat the treatment one week later to prevent reinfection, and repeat weekly as necessary — skipping this step virtually guarantees reinfestation from newly hatched larvae
Plant Safety
Fritz states plainly that Expel-P does not harm the bio-filter, plants, other invertebrates or uninfected fish. It is safe to run in a planted display.
Invertebrate Safety
Generally safe for invertebrates at recommended doses, owing to differences in vertebrate and invertebrate nAChR subunit composition. Fritz notes two specific exceptions: tube worms and feather dusters may be negatively affected, and some snail species may be temporarily affected. Levamisole is also used deliberately as a coral dip for flatworms and pest nudibranchs.
At a glance
- Manufacturer
- Fritz Aquatics
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.