Fenbendazole

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Fenbendazole (dewormer) - (updated 9-14-22)

What It Treats Flukes (Monogeneans) and intestinal worms*. Fenbendazole is particularly useful to treat flukes & intestinal worms which seem resistant to praziquantel.

How To TreatFenbendazole is a drug often prescribed by veterinarians to treat intestinal parasites in dogs & cats (sometimes sold as Panacur). It is also effective to use on fish and can be purchased online here: Fenbendazole

Or NFP Fenbendazole is resold in smaller quantities here & here.

Noga discusses using fenbendazole to treat monogeneans (flukes) in his book Fish Disease: Diagnosis and Treatment 2nd Edition. He recommends a 12 hour bath treatment at 25 mg/L (95 mg/gallon). Heavily aerate + temp control the bath water. Fully dissolve the medication before adding fish. Fenbendazole is not easily water soluble, so I advise using either ethyl alcohol or preferably DMSO to aid with dissolving it: How To - Use DMSO to dissolve medications

I advise transferring the fish into a new QT following each bath treatment (to prevent reinfection). You will also need to administer a second bath + transfer about a week later in order to eliminate any hatchlings. It is best to use this treatment calendar to determine when is the best time to do the second bath: Marine Parasites
For treating intestinal worms*, Noga recommends dosing fenbendazole into a QT at 2 mg/L (7.6 mg/gallon) once/week for 3 weeks. However, you can also try lacing fish food with fenbendazole in addition to dosing the water column. (DO NOT dose or food soak fenbendazole in a reef environment.) You’ll need to use a binder (e.g. Seachem Focus, unflavored gelatin, Agar) to reduce the loss of medication to the water through diffusion. I recommend feeding fenbendazole for 2-3 weeks, or until symptoms are no longer present. My recipe for food soaking deworming medications can be found below:

Using a shot glass:
  • 1 tbsp food (preferably pellets or frozen food)
  • 1 scoop (~ 1/8 teaspoon) of medication
  • 1-2 scoops Seachem Focus* (binder that also makes it reef safe)
  • A pinch of Epsom salt to help expel dead worms/parasites
  • A few drops of saltwater or fish vitamins
  • Stir until a medicated food slurry has been achieved
  • Feed after soaking for 30 mins
  • Refrigerate or freeze any leftovers for future use
  • You can feed this mix 1-2 times per day. Not recommend to exceed 2 feedings per day with medicated food.
  • Feed daily for 2-3 weeks, or until poop returns to a solid brown or green color (no white).
* Agar or unflavored gelatin can be used in lieu of Focus. More medicated food recipes can be found here: How To Make Medicated Feed - Hikari Sales USA

ProsHighly effective dewormer

Cons/Side Effects:
  1. Some fish will act "off" for 24-48 hours after treating with Fenbendazole and may not eat.
  2. However, @Dierks reports that wrasses are the only fish he has ever lost after treating with Fenbendazole.
  3. Fenbendazole is NOT reef safe. Not even when soaked in food.
More info on Fenbendazole from seahorse.com: Fenbendazole (Panacur) | Seahorse.com
 
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Dierks

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Also note that if you are going to do the bath and dissolve the Fenbendazole be careful with Wrasses. If you do have a fish that does not take the Fenbendazole bath well I personally have had success with the Methylene Blue Bath to detox them.
 
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We used it at first with focus in the DT and believe that it eventually killed a leather a month after first using even though there was only a few feedings, then moved fishies to a QT. We have a mushroom that totally consumed food with bendazole and prazi pro after it landed on it and it’s still alive. We also believe that a small acan colony looked like it was dying but appears to be bouncing back 3mth later.

I think our fish would still have intestinal issues if it wasn’t for this because GC didn’t appear to be working. In the qt tank we did not use focus and fish seemed more eager to eat food and didn’t want anything to do with focus.
Never dosed tank only mixed with food.
 

Dierks

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Also added this to the sticky: Using a drop or two of Dimethyl sulfoxide (DMSO) will help to fully dissolve Fenbendazole in a cup before dosing.
I finally made a contribution that made it onto a sticky!! 😄(y) I personally use 135 mg/ml for DMSO.
 

rickc

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I have used fenbendazole in a reef. It will kill all octocorals. Does a great job on getting rid of pesky Xenia, GSP and other octocorals. It also kills bristle worms, some snails (I don't remember which ones live and which ones die so remove all) and it also kills hydroids. The tank had SPS and LPS and the dreaded pest Xenia. It has no effect on the SPS and LPS. If the tank is mature expect to see a massive die off of bristle worms and be ready to vacuum them out daily if not more.

I used powerhead to blast the rock and sand to get the fenbendazole into the water stream so that it could be removed with micro filtration and carbon. I kept the snails out for 2 months and reintroduced with no issue.

If you like your octocorals, do not use. If you want to rid you tank of these, it will work as stated. It takes several days to see the effect, but be ready for ammonia and nitrite spikes.
 
Up front: I’m new to saltwater tanks.

My clownfish had white stringy poop and Prazi didn’t work. I used Fenbendazole in their food for 3 weeks and 1 week later transferred several coral I had in 76 day QT into my DT with the clownfish. 3 weeks later both leather coral died. Now I’m scared to put any coral in my DT. I see you used carbon and “micro filtration” and waited 2 months before putting snails back in. 1) What is “micro filtration”? A sock? 2) Do you think 2 months would be safe for coral? The Fenbendazole didn’t kill any of my snails, just the leathers (toadstool and devil's hand). Thanks in advance.
 

Humblefish

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Up front: I’m new to saltwater tanks.

My clownfish had white stringy poop and Prazi didn’t work. I used Fenbendazole in their food for 3 weeks and 1 week later transferred several coral I had in 76 day QT into my DT with the clownfish. 3 weeks later both leather coral died. Now I’m scared to put any coral in my DT. I see you used carbon and “micro filtration” and waited 2 months before putting snails back in. 1) What is “micro filtration”? A sock? 2) Do you think 2 months would be safe for coral? The Fenbendazole didn’t kill any of my snails, just the leathers (toadstool and devil's hand). Thanks in advance.

Micro filtration probably means filter floss or a pad, or possible a poly filter like this: https://www.poly-bio-marine.com

A poly filter supposedly removes, "Medication such as Copper Sulphate and Formalin, Quinine Sulphate, Malachite Green, chelated copper compounds and even antibiotics used to treat bacterial infections" according to their website. So, I'd be pretty confident it could also remove fenbendazole.

But let's see if @rickc will chime in to verify this.
 

DexterB

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Personal experience- I used double amount of Focus to try to bind, did water change, ran carbon etc. But lost all soft corals when dosing Fendbendazole to my fish in medicated food.
 
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Like the article stated it’s safe for mushrooms, we had a large piece of food soaked with Fendbendazole land on a mushroom, closed up immediately consuming it and to this day lives on as our leather didn’t make it but an Acan colony is trying to recover months later.

Very interesting about the rock!
 
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