rockpaper
New Member
So I am new to these forums, and I've been working on my first planted tank. I posted a reply in that thread about how I was trying to deal with a hydra infestation. Basically, because I had no livestock, I had many cyclops that were subsequently eaten by many, many hydra. Because I want to keep fish with an appetite for a lot of small, live foods, I decided I needed to get rid of the hydra before I gave myself a giant outbreak. (In case anyone is curious, I have my nerite temporarily living in a glass 4 L vase with a sponge filter, algae rocks, and a heater).
The most commonly cited treatments for hydra are No Planaria and Fenbendazole. It seems like it used to be common to try praziquantel (ineffective) and flubendazole (hard to get, especially over here in the USA), but these are less and less often recommended. I don't have any experience with No Planaria because I chose to treat with Fenbendazole, but over the course of prepping for the treatment I found a lot of information that I thought might be useful for others. This information will also be useful for individuals considering using fenbendazole for any anthelmintic purposes, such as for treatment of planaria or flukes, among other uses.
To give context, I am a molecular biologist with experience working in plant, bacterial, fungal, mammalian, and planarian labs (and others...). I am reporting on this information because I see many people posting on (usually other) forums using information that doesn't check out when reviewing research and industrial literature, especially in regards to its persistence in the tank and toxicity to our livestock, plants, and microorganisms. I want people to feel educated and confident if and when they choose to use fenbendazole for treatment of internal or external tank parasites.
2007 USDA Petition to Amend 7 CFR § 205.603(a)(12) To Include Fenbendazole As A Synthetic Substance Allowed for Use in Organic Livestock Production -- Link
In this petition, the degradation times, toxicity, metabolic by-products, and considerations for avoiding anthelmintic resistance of fenbendazole are discussed at length. Because this is a lengthy document, I will only be referencing the pages of the summary petition in the first 30 pages, and almost exclusively the information in pages 5-21, since the rest of the petition involves research in cattle. I am sure that is very useful and interesting for the farmers and regulators, but not so for us!
Degradation times: Although fenbendazole is not efficiently biodegraded in sewage effluent (pg. 7), it rapidly degrades when exposed to light (pg. 9). This degradation is pH dependent; at pH 7, fenbendazole has a half life in light conditions of 0.527 days. At pH 5, that time increases to 0.713 days. In either case, one can expect that fenbendazole will be fully decomposed after several days of lighted conditions. This directly counters the narrative I often see where people are concerned that fenbendazole will continue to be present in their tanks for months after treatment. This assessment is restated in No significant impact on aquatic environment on pg. 12, stating "the half life [of fenbendazole] in water is less than one day".
It is worth noting that there are some caveats here:
Toxicity in mammals: Only mammals were tested for toxicity studies in this petition (pg. 14). For acute toxicity, all mammals they tested had a higher toxic dose than 500 mg/kg (500 ppm in-body). Interestingly, the mammals that had the lowest tolerance of the drug (500 mg/kg) were dogs-- the very animals Panacur C is approved to treat! For chronic toxicity, they tested rats and dogs with 60-day exposures to one-quarter the acute toxic doses for each species. This exposure was not found to harm the animals while alive, nor were any post-mortem effects observed.
Toxicity in aquatic organisms: Since the petition did not specifically explore toxicity to common aquatic organisms, I went looking for more information in other literature. One 2015 study explored the toxicity in V. fischeri, green algae, duckweed, and daphnia. The acute toxicity doses in these organisms was much lower than in mammals; daphnia in particular experienced toxicity with an effective dose of only 0.019 mg/L (0.019 ppm).V. fischeri also had a low effective toxicity dose of >0.3 mg/L (ppm), but the rest of the examined organisms were fine into concentrations of >1 mg/L (ppm).
Another study from 2020 explored the use of dietary fenbendazole for treatment of gill parasites in carp (Labeo rohita) and found that the most effective treatment was a course of 20 mg/kg body weight fenbendazole delivered via food on days 0, 3, 7. Under this treatment, all gill parasites were eliminated by day 15-- but the authors did mention that they were able to observe oxidative stress in the treated carp (read: if your fish isn't doing good already, this much of a treatment might be enough to tip them into the grave).
Toxicity in plants: On pgs. 17-19, they explored the concentrations necessary to cause reactions in a number of terrestrial plants. These plants were potted in inert sand and watered with a nutrient + fenbendazole solution of various concentrations. Although they didn't test any of the plants we are likely to use in our aquariums, they saw no effect on any plants they tested in concentrations near 1 g/kg (1 g/L)... except weirdly for tomatoes? Tomatoes exhibited effects related to toxicity concentrations of at 64 mg / kg (64 mg / L), which-- while very low by comparison to the other plants-- is still well above the thresholds we treat our tanks with.
Toxicity in other organisms: Going back to the USDA petition, they assessed whether fenbendazole had toxic effects to other organisms from various branches of life. The short answer is that no organisms they list on pg. 19-21 were affected by fenbendazole in their toxicity assays. I don't want to detail all of the organisms they tested, but the list includes Gram negative and Gram positive bacteria, protozoa, mycoplasma, and fungi.
Some key takeaways:
In summary:
Based on reading this information, I am confident that fenbendazole is a relatively safe means of handling parasitic infections. I do not believe it is likely to harm our biological filter, nor is it likely to harm our livestock or plants at the doses we use in the aquarium. I also suspect that many fish or shrimp deaths reported by people who have used fenbendazole may be due to either 1) pre-existing stress or medical conditions in the livestock that are exacerbated by the oxidative stress brought on by fenbendazole, 2) a nitrogenous waste spike and water quality plummet from the sudden death of many (now decomposing) parasites and worms, or 3) severe overdosing-- but this last one is unlikely given the large acceptable range of doses in tested organisms. I also believe that fenbendazole can be eliminated from most home aquariums using time, bright lighting, and prudent water changes and substrate cleaning. When I complete my fenbendazole dosing, I intend on using carbon and Purigen in my filter, but I don't really think this will be the deciding factor on whether fenbendazole is effectively removed from my tank.
I intend on coming back to this thread and updating it with information about how my personal experience went while dosing fenbendazole for hydra in my tank. Hopefully, though, this "anecdote-free" summary of some information available about fenbendazole and its toxicity will be useful to others on this forum!
EDIT: OH! But it does probably kill nerite snails! Keep your snails safe folks 😉
The most commonly cited treatments for hydra are No Planaria and Fenbendazole. It seems like it used to be common to try praziquantel (ineffective) and flubendazole (hard to get, especially over here in the USA), but these are less and less often recommended. I don't have any experience with No Planaria because I chose to treat with Fenbendazole, but over the course of prepping for the treatment I found a lot of information that I thought might be useful for others. This information will also be useful for individuals considering using fenbendazole for any anthelmintic purposes, such as for treatment of planaria or flukes, among other uses.
To give context, I am a molecular biologist with experience working in plant, bacterial, fungal, mammalian, and planarian labs (and others...). I am reporting on this information because I see many people posting on (usually other) forums using information that doesn't check out when reviewing research and industrial literature, especially in regards to its persistence in the tank and toxicity to our livestock, plants, and microorganisms. I want people to feel educated and confident if and when they choose to use fenbendazole for treatment of internal or external tank parasites.
2007 USDA Petition to Amend 7 CFR § 205.603(a)(12) To Include Fenbendazole As A Synthetic Substance Allowed for Use in Organic Livestock Production -- Link
In this petition, the degradation times, toxicity, metabolic by-products, and considerations for avoiding anthelmintic resistance of fenbendazole are discussed at length. Because this is a lengthy document, I will only be referencing the pages of the summary petition in the first 30 pages, and almost exclusively the information in pages 5-21, since the rest of the petition involves research in cattle. I am sure that is very useful and interesting for the farmers and regulators, but not so for us!
Degradation times: Although fenbendazole is not efficiently biodegraded in sewage effluent (pg. 7), it rapidly degrades when exposed to light (pg. 9). This degradation is pH dependent; at pH 7, fenbendazole has a half life in light conditions of 0.527 days. At pH 5, that time increases to 0.713 days. In either case, one can expect that fenbendazole will be fully decomposed after several days of lighted conditions. This directly counters the narrative I often see where people are concerned that fenbendazole will continue to be present in their tanks for months after treatment. This assessment is restated in No significant impact on aquatic environment on pg. 12, stating "the half life [of fenbendazole] in water is less than one day".
It is worth noting that there are some caveats here:
- This section of the petition is non-specific about the light intensity, wavelength, etc., meaning that the actual degradation times may be longer in-practice. For most of us here at UKAPS, we often have full-spectrum, intense lighting so as to best grow our plants-- but if you have a specifically low-light or short-photoperiod tank, it may take longer
- Photoperiod is also an important consideration-- presumably, these tests were done with continuously lighting. 24 hours of lighting is several days of aquarium light-cycle; consider your photoperiod when considering how long it will take to degrade the fenbendazole.
- Fenbendazole does appear to bind tightly to soils in some conditions (pg. 13-14), and presumably some particles will fall into our substrates and have less exposure to light. To me, this indicates that the usual recommendation of a thorough gravel vacuuming is a logically-sound practice, especially if fenbendazole particles locked in the substrate are exposed to light for photolytic decomposition.
Toxicity in mammals: Only mammals were tested for toxicity studies in this petition (pg. 14). For acute toxicity, all mammals they tested had a higher toxic dose than 500 mg/kg (500 ppm in-body). Interestingly, the mammals that had the lowest tolerance of the drug (500 mg/kg) were dogs-- the very animals Panacur C is approved to treat! For chronic toxicity, they tested rats and dogs with 60-day exposures to one-quarter the acute toxic doses for each species. This exposure was not found to harm the animals while alive, nor were any post-mortem effects observed.
Toxicity in aquatic organisms: Since the petition did not specifically explore toxicity to common aquatic organisms, I went looking for more information in other literature. One 2015 study explored the toxicity in V. fischeri, green algae, duckweed, and daphnia. The acute toxicity doses in these organisms was much lower than in mammals; daphnia in particular experienced toxicity with an effective dose of only 0.019 mg/L (0.019 ppm).V. fischeri also had a low effective toxicity dose of >0.3 mg/L (ppm), but the rest of the examined organisms were fine into concentrations of >1 mg/L (ppm).
Another study from 2020 explored the use of dietary fenbendazole for treatment of gill parasites in carp (Labeo rohita) and found that the most effective treatment was a course of 20 mg/kg body weight fenbendazole delivered via food on days 0, 3, 7. Under this treatment, all gill parasites were eliminated by day 15-- but the authors did mention that they were able to observe oxidative stress in the treated carp (read: if your fish isn't doing good already, this much of a treatment might be enough to tip them into the grave).
Toxicity in plants: On pgs. 17-19, they explored the concentrations necessary to cause reactions in a number of terrestrial plants. These plants were potted in inert sand and watered with a nutrient + fenbendazole solution of various concentrations. Although they didn't test any of the plants we are likely to use in our aquariums, they saw no effect on any plants they tested in concentrations near 1 g/kg (1 g/L)... except weirdly for tomatoes? Tomatoes exhibited effects related to toxicity concentrations of at 64 mg / kg (64 mg / L), which-- while very low by comparison to the other plants-- is still well above the thresholds we treat our tanks with.
Toxicity in other organisms: Going back to the USDA petition, they assessed whether fenbendazole had toxic effects to other organisms from various branches of life. The short answer is that no organisms they list on pg. 19-21 were affected by fenbendazole in their toxicity assays. I don't want to detail all of the organisms they tested, but the list includes Gram negative and Gram positive bacteria, protozoa, mycoplasma, and fungi.
Some key takeaways:
- The tested concentrations was 0.1 mg/mL, meaning that they tested for toxicity in these organisms at 1000x the concentration we usually use in our tanks
- They did not test for effects on Nitrobacter, Nitrosomonas, or Nitrospira genera. I personally don't think fenbendazole is likely to affect our biological filter, but I don't want to mislead you into thinking this petition 100% sorted out that issue.
In summary:
Based on reading this information, I am confident that fenbendazole is a relatively safe means of handling parasitic infections. I do not believe it is likely to harm our biological filter, nor is it likely to harm our livestock or plants at the doses we use in the aquarium. I also suspect that many fish or shrimp deaths reported by people who have used fenbendazole may be due to either 1) pre-existing stress or medical conditions in the livestock that are exacerbated by the oxidative stress brought on by fenbendazole, 2) a nitrogenous waste spike and water quality plummet from the sudden death of many (now decomposing) parasites and worms, or 3) severe overdosing-- but this last one is unlikely given the large acceptable range of doses in tested organisms. I also believe that fenbendazole can be eliminated from most home aquariums using time, bright lighting, and prudent water changes and substrate cleaning. When I complete my fenbendazole dosing, I intend on using carbon and Purigen in my filter, but I don't really think this will be the deciding factor on whether fenbendazole is effectively removed from my tank.
I intend on coming back to this thread and updating it with information about how my personal experience went while dosing fenbendazole for hydra in my tank. Hopefully, though, this "anecdote-free" summary of some information available about fenbendazole and its toxicity will be useful to others on this forum!
EDIT: OH! But it does probably kill nerite snails! Keep your snails safe folks 😉
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