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Fish Medic
Using Praziquantel (PZQ) to treat flukes
Overview
In the early 1990’s, a researcher at the New York Aquarium published a paper on using Praziquantel (PZQ) to help control flukes, a parasitic flatworm. Also known as monogenean trematodes, these fish parasites can cause significant mortality in aquarium fish. It is also used orally to treat tapeworms. It has limited to no effect on other parasites. The mechanism of Praziquantel’s action seems to be that it causes the flukes to temporarily relax, allowing them to be dislodged from the fish. Once that happens, the adult fluke is unable to reattach, and it dies.
Basic dosing and application
To treat with Praziquantel, calculated the volume of water in the tank (L" x W" x H") divided by 231 to get US gallons. If the tank has rocks and sand in it, deduct 15% to offset water displacement (multiply by 0.85). Remove any carbon, turn off any UV, add a good air stone, keep any skimmer running, but disable the collection cup, or let it flow back into the tank.
The standard dose is 2.2 mg/l to 2.5 mg/l for 24 hours. There is also a 10 mg/l three hour dip and a 6 mg/l six hour dip. When using PZQ as a dip, the fish must be moved into a new tank at the conclusion of the dip. Moving the fish back into the tank it came from just allows for reinfection.
For non-metric system dosing, the calculation is: tank volume in US gallons multiplied by the dose in mg/l divided by 264.
Praziquantel powder is barely soluble in seawater. It needs to be dispersed as a fine particulate. One way to do that is to use a solvent (Propylene glycol or alcohol - don't use DMSO though, that isn't tested well enough). When you add the dissolved PZQ into the tank, you'll see it come out as a fine suspension when it hits the water - it gets dispersed that way. The trouble is these solvents can cause bacterial blooms. So - using a baby brine shrimp net or other fine material (even pantyhose will work) and then rinsing/pushing the powder through that into the tank is a better option. There are some fine nylon mesh available online that works as well as baby brine shrimp nets.
Timing the repeat doses
Multiple doses are required when using PZQ in order to break the life cycle of various species of flukes. PZQ does not kill fluke eggs or larva, so the timing needs to be spaced out to allow for all eggs to hatch and grow into young flukes, but then cause those flukes to drop off the fish before they can produce new eggs of their own. Cooler water temperature slows this process and warmer water speeds it up. There is also variation in species, as well as variation in a given population – so obviously, this is a major drawback in using PZQ to control flukes. Estimated timing is as follows:
Live bearing Gyrodactylus flukes are the easiest to control as they have no egg stage. Two PZQ additions, 48 hours apart is typically sufficient to eradicate this type of fluke. However, these are rarely seen in marine aquarium fish.
Egg laying Dactylogyrids are the common gill fluke in marine aquarium fish. Repeat doses to control this parasite is usually around 5 days, with three treatments required.
Egg laying Capsalids (Neobenedenia) are large flukes (the only ones that can be seen by the naked eye) and their eggs are very tough and sticky. Up to five doses, 8 days apart are required to control this parasite. In fish-only systems, hyposalinity (half salinity; 16 ppt or 1.012) is a better treatment option.
Encysted Digenean flukes and Turbellarians are not well controlled by PZQ, as they live inside cysts, so although they are temporarily incapacitated by PZQ, they do not fall off the fish and then they can recover and continue their parasitic life.
Tapeworms (cestodes) can be controlled with oral PZQ, but other internal parasites are not. There is evidence that a proper oral dose can also control digenean flukes which are not controlled by PZQ baths. The proper dose is 50 mg PZQ per 1 KG of fish body mass. You CANNOT just mix PZQ with Focus in uncontrolled amounts. This article describes how to administer medicated foods properly: https://www.reef2reef.com/ams/proper-dosing-of-medicated-foods.780/
Drawbacks to using Praziquantel
Some people report their fish don’t feed well after PZQ treatments. Wrasses are commonly reported to be sensitive to these treatments. In both of these cases, a lack of aeration or the solvent used seems to be the root cause.
Bacterial degradation is a huge problem with multiple doses of PZQ. Each time PZQ is dosed, bacteria begin to consume it, As they do so, they multiply. Each subsequent treatment then becomes effective for less and less time. You can dose 3 to 5 times before the PZQ is pretty much rendered useless. The dose can be increased to compensate, that that's risky since you cannot really tell how much is being decomposed. Praziquantel, and the solvent in Prazipro is rapidly broken down by bacteria. The first dose is assimilated in about 36 hours, the second dose in perhaps 24 hours, then each successive dose gets consumed faster by the bacteria. After about five or six doses, the bacteria eat it faster than it can even work. Nobody really knows how long the heterotrophic bacteria remain hyperactive after they have grown to consume PZQ - but it is at least 4 months (personal experience). Most people sterilize the treatment tank and reset it if they plan to run multiple PZQ treatments.
PZQ and other products It is best to not use carbon, ozone of UV water treatments within 36 hours of dosing PZQ. Protein skimmers should be continued, but don't collect the skimmate. Carbon dosing products, such as NoPox are a blend of carbon sources (ethanol, acetic acid and others?) that serve as a carbon source for bacteria, the same way that PZQ and its solvents (ethanol or glycol) do. Carbon dosing should be stopped prior to dosing with PZQ, and and not continued again until the treatment is completed.
Products reported to contain Praziquantel
Please be aware that companies can and do change their formulations with no notice. This information is current when written in 2025, but it is always a good idea to confirm the product’s use with the manufacturer.
General Cure (GC): The problem with GC is that metronidazole and PZQ have different dosing schedules! Metro is 25 mg/l every other day for three treatments and PZQ is 2.2 mg/l every 5 to 8 days for three treatments. The metronidazole component is also NOT reef safe. Do not use this product in oral formulations, as the oral dose for these two medications are different and cannot be combined.
Prazicleanse supplies 2.5 ppm PZQ and they suggest to dose it on a 5 day interval (might be a bit too quick for Neobenedenia). There is no metronidazole or solvents in this product. This product needs to be dispersed through a fine mesh net and mixed with freshwater and then added to the tank. Do NOT use a solvent like ethanol or DMSO, as that just gets you into the issues seen with Prazipro and bacterial blooms.
Paracleanse is essentially the same as General Cure. It contains Metronidazole and Praziquantel. It uses an every second day for three times treatment which is how metronidazole is used. They say it is "safe for invertebrates" but I wouldn't use it with marine invertebrates due to the metronidazole. It is a lower dose of PZQ, at 2 ppm. That is below the usual minimum dose of 2.2 ppm. Paracleanse is an older product.
Prazipro: The glycol solvent in the Prazipro causes the organic loading - it’s kind of like carbon dosing. Stop any additional carbon dosing. Run any skimmer, but don’t collect the skimmate. Adding extra aeration is important. Bacteria grows and consumes both PZQ and the solvent. This bacteria really goes after PZQ and persists for months after treatments. Each treatment with PZQ causes more bacteria to grow. Eventually the bacteria consume the PZQ before it really can work. This happens around the fourth or fifth treatment.
A published European formulary lists products containing Praziquantel, but some are no longer available due to changing laws in the EU:
Dactymor
eSHA gdex
Fluke P
Fluke- Solve
Gyrodol Plus
Tremazol
Dosing any of these products properly would require knowing the concentration of Praziquantel in the product, and then calculating the dose to ensure it is within the proper range (typically 2.2 to 2.5 ppm for a standard dose).
Overview
In the early 1990’s, a researcher at the New York Aquarium published a paper on using Praziquantel (PZQ) to help control flukes, a parasitic flatworm. Also known as monogenean trematodes, these fish parasites can cause significant mortality in aquarium fish. It is also used orally to treat tapeworms. It has limited to no effect on other parasites. The mechanism of Praziquantel’s action seems to be that it causes the flukes to temporarily relax, allowing them to be dislodged from the fish. Once that happens, the adult fluke is unable to reattach, and it dies.
Basic dosing and application
To treat with Praziquantel, calculated the volume of water in the tank (L" x W" x H") divided by 231 to get US gallons. If the tank has rocks and sand in it, deduct 15% to offset water displacement (multiply by 0.85). Remove any carbon, turn off any UV, add a good air stone, keep any skimmer running, but disable the collection cup, or let it flow back into the tank.
The standard dose is 2.2 mg/l to 2.5 mg/l for 24 hours. There is also a 10 mg/l three hour dip and a 6 mg/l six hour dip. When using PZQ as a dip, the fish must be moved into a new tank at the conclusion of the dip. Moving the fish back into the tank it came from just allows for reinfection.
For non-metric system dosing, the calculation is: tank volume in US gallons multiplied by the dose in mg/l divided by 264.
Praziquantel powder is barely soluble in seawater. It needs to be dispersed as a fine particulate. One way to do that is to use a solvent (Propylene glycol or alcohol - don't use DMSO though, that isn't tested well enough). When you add the dissolved PZQ into the tank, you'll see it come out as a fine suspension when it hits the water - it gets dispersed that way. The trouble is these solvents can cause bacterial blooms. So - using a baby brine shrimp net or other fine material (even pantyhose will work) and then rinsing/pushing the powder through that into the tank is a better option. There are some fine nylon mesh available online that works as well as baby brine shrimp nets.
Timing the repeat doses
Multiple doses are required when using PZQ in order to break the life cycle of various species of flukes. PZQ does not kill fluke eggs or larva, so the timing needs to be spaced out to allow for all eggs to hatch and grow into young flukes, but then cause those flukes to drop off the fish before they can produce new eggs of their own. Cooler water temperature slows this process and warmer water speeds it up. There is also variation in species, as well as variation in a given population – so obviously, this is a major drawback in using PZQ to control flukes. Estimated timing is as follows:
Live bearing Gyrodactylus flukes are the easiest to control as they have no egg stage. Two PZQ additions, 48 hours apart is typically sufficient to eradicate this type of fluke. However, these are rarely seen in marine aquarium fish.
Egg laying Dactylogyrids are the common gill fluke in marine aquarium fish. Repeat doses to control this parasite is usually around 5 days, with three treatments required.
Egg laying Capsalids (Neobenedenia) are large flukes (the only ones that can be seen by the naked eye) and their eggs are very tough and sticky. Up to five doses, 8 days apart are required to control this parasite. In fish-only systems, hyposalinity (half salinity; 16 ppt or 1.012) is a better treatment option.
Encysted Digenean flukes and Turbellarians are not well controlled by PZQ, as they live inside cysts, so although they are temporarily incapacitated by PZQ, they do not fall off the fish and then they can recover and continue their parasitic life.
Tapeworms (cestodes) can be controlled with oral PZQ, but other internal parasites are not. There is evidence that a proper oral dose can also control digenean flukes which are not controlled by PZQ baths. The proper dose is 50 mg PZQ per 1 KG of fish body mass. You CANNOT just mix PZQ with Focus in uncontrolled amounts. This article describes how to administer medicated foods properly: https://www.reef2reef.com/ams/proper-dosing-of-medicated-foods.780/
Drawbacks to using Praziquantel
Some people report their fish don’t feed well after PZQ treatments. Wrasses are commonly reported to be sensitive to these treatments. In both of these cases, a lack of aeration or the solvent used seems to be the root cause.
Bacterial degradation is a huge problem with multiple doses of PZQ. Each time PZQ is dosed, bacteria begin to consume it, As they do so, they multiply. Each subsequent treatment then becomes effective for less and less time. You can dose 3 to 5 times before the PZQ is pretty much rendered useless. The dose can be increased to compensate, that that's risky since you cannot really tell how much is being decomposed. Praziquantel, and the solvent in Prazipro is rapidly broken down by bacteria. The first dose is assimilated in about 36 hours, the second dose in perhaps 24 hours, then each successive dose gets consumed faster by the bacteria. After about five or six doses, the bacteria eat it faster than it can even work. Nobody really knows how long the heterotrophic bacteria remain hyperactive after they have grown to consume PZQ - but it is at least 4 months (personal experience). Most people sterilize the treatment tank and reset it if they plan to run multiple PZQ treatments.
PZQ and other products It is best to not use carbon, ozone of UV water treatments within 36 hours of dosing PZQ. Protein skimmers should be continued, but don't collect the skimmate. Carbon dosing products, such as NoPox are a blend of carbon sources (ethanol, acetic acid and others?) that serve as a carbon source for bacteria, the same way that PZQ and its solvents (ethanol or glycol) do. Carbon dosing should be stopped prior to dosing with PZQ, and and not continued again until the treatment is completed.
Products reported to contain Praziquantel
Please be aware that companies can and do change their formulations with no notice. This information is current when written in 2025, but it is always a good idea to confirm the product’s use with the manufacturer.
General Cure (GC): The problem with GC is that metronidazole and PZQ have different dosing schedules! Metro is 25 mg/l every other day for three treatments and PZQ is 2.2 mg/l every 5 to 8 days for three treatments. The metronidazole component is also NOT reef safe. Do not use this product in oral formulations, as the oral dose for these two medications are different and cannot be combined.
Prazicleanse supplies 2.5 ppm PZQ and they suggest to dose it on a 5 day interval (might be a bit too quick for Neobenedenia). There is no metronidazole or solvents in this product. This product needs to be dispersed through a fine mesh net and mixed with freshwater and then added to the tank. Do NOT use a solvent like ethanol or DMSO, as that just gets you into the issues seen with Prazipro and bacterial blooms.
Paracleanse is essentially the same as General Cure. It contains Metronidazole and Praziquantel. It uses an every second day for three times treatment which is how metronidazole is used. They say it is "safe for invertebrates" but I wouldn't use it with marine invertebrates due to the metronidazole. It is a lower dose of PZQ, at 2 ppm. That is below the usual minimum dose of 2.2 ppm. Paracleanse is an older product.
Prazipro: The glycol solvent in the Prazipro causes the organic loading - it’s kind of like carbon dosing. Stop any additional carbon dosing. Run any skimmer, but don’t collect the skimmate. Adding extra aeration is important. Bacteria grows and consumes both PZQ and the solvent. This bacteria really goes after PZQ and persists for months after treatments. Each treatment with PZQ causes more bacteria to grow. Eventually the bacteria consume the PZQ before it really can work. This happens around the fourth or fifth treatment.
A published European formulary lists products containing Praziquantel, but some are no longer available due to changing laws in the EU:
Dactymor
eSHA gdex
Fluke P
Fluke- Solve
Gyrodol Plus
Tremazol
Dosing any of these products properly would require knowing the concentration of Praziquantel in the product, and then calculating the dose to ensure it is within the proper range (typically 2.2 to 2.5 ppm for a standard dose).
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