identification and treatment for monogenean oncomiracidium fluke on Paracanthurus tang

Peter Houde

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I would greatly appreciate your advice regarding the identification of and treatment for a "fluke" that has recently infested my tank and Paracanthurus tang.

I have a marine aquarium that is heavily infested with some form of monogeneans. One fish exhibits overt disease ("blue tang", Acanthuridae: Paracanthurus hepatus; probable infestation of cornea, loss of color in facial region, deterioration of dorsal and caudal fins possibly due to secondary infection). Several other fish are seemingly unaffected (including 15-20 yr old clownfish), but a damselfish that permanently lost facial color many years ago may have been harboring parasites all along. It also has some tattering of pectoral and caudal fins, and both it and a mandarin have developed small (<1 mm) unequally sized white spots within the last days since I began treatment (described below). The tang's behavior is normal. It does "twitch" but this seems to be only in response to human proximity/close observation; it does not seem to twitch when observed from a distance and it does not rub or scratch itself on objects. None of the fish do. None of the fish show labored breathing. I am anxious to identify the parasite at least at a taxonomic level that will help me to decide the best method of treatment, both for the fish and the entire aquarium.

Tank: established >25 years; fish only; 473 liters; temperature 78F, 25.5C; specific gravity typically 1.024 (but currently 1.018, please see below); nitrate ca. 15 mg/l; no ammonia or nitrite test but pH 8.15 and NO3 suggest this isn't an issue; no copper test but no conceivable source of copper; phosphate ~0.32 (Hanna spec; lower by Salifert and Reef Master tests); KH/Alk 10.33-10.5 (Salifert; 9-10 by Reef Master); Ca 430 ppm (Salifert: 380 by Reef Master); Mg 1290; biological filtration (bio-balls in sump, 5-6 cm coral gravel, abundant purple coralline algae, and Gracilaria, Chaetomorpha, and Penicillus macros) and protein skimmer. I apologize the image of my aqarium is not a full view but it is representative of the whole tank.
Inhabitants: 2 Amphiprion ocellaris, 1 Chrysiptera parasema, 1 Pseudochromis paccagnellae, 1 Synchiropus splendidus, 1 Paracanthurus hepatus, various snails (cerithiids, Neritina, Nasarius, unidentified), emerald crabs, bristle worms, tube worms, unidentified worms, more bristle worms, unidentified colonial tunicates, unidentified encrusting sponges, amphipods, copepods, and things that mysteriously come and go as if by spontaneous generation - now to include monogeneans.

It is not practical for me to capture the afflicted tang (though I've not ruled out the possibility entirely), so I have not been able to examine adult parasites. I also have not observed eggs. However, oncomiracidia were suddenly frighteningly abundant on the aquarium glass. None can be found still 2 days after water change and glass cleaning, but I refuse to believe that they are not all over the live rock. I check the glass regularly for copepods and I've never seen oncomiracidia before. I recorded a video that is decidedly of better clarity than the attached still photo, but at 139 Mb the video is too large to upload. You can access it if you wish on my server at:

http://lithornis.nmsu.edu/~phoude/oncomiracidium 139 Mb.MOV

There are a few characteristics I can describe. It is at least somewhat shorter and much narrower than an adult copepod, e.g., Tisbe. It is ciliated on what I interpret as its dorsal side. There are very long and pronounced cilia around its anterior end that beat synchronously and continuously and extend deeply into its pharynx or caecum. The caudal-most cilia are also elongate. It has no eye spots and no anchor hooks that I can discern, so I do not believe this is Neobenedenia even if that is the most common scourge of marine aquaria. The oncomiracidia on the glass of the aquarium are considerably more elongate than the one in my image, and they are quite active. Under the microscope they become shorter in length and soon disintegrate, possibly killed by the focused microscope light.

Question: Can you identify this to a level that would assist in determining the best treatment?

Question: I dosed the tank once with praziquantel to a concentration of 2.5 mg/l (on 2021/02/27) given my crude estimate of tank water volume after displacement by gravel and live rock. I've been supplementing frozen food diet (San Fransisco mysis, brine shrimp, and Emerald Entree, and Ocean Nutrition Formula 2) with metronidazole (SeaChem Metroplex) and nitrofurantoin (SeaChem Focus) garlic extract and Brightwell's Aminomega daily for 3-4 weeks. I have read some conflicting information regarding the appropriate dosing of praziquantel that I hope you can arbitrate. Hikari's Prazipro recommends dosing of 2.5 mg/l with the potential for re-dosing in 5-7 days but as early as 3 days, and that seems to be the popular opinion. However, several published references suggest that 2.5 mg/l should be added every 2 days until 10 mg/l is reached. I'd appreciate advice on protocol or alternative treatments.

Question: Reefs.com (Joe Rowlett) advocates reducing salinity to 15 ppt for 5 days (specific gravity 1.011), citing several studies on its effectiveness for treating for Neobenedenia. One of those references specifically found 18 ppt (SG 1.013) ineffective. That frightens me. Is 15 ppt safe for fish? Is it safe for snails, crabs, coralline algae, copepods, etc? (no live corals) Marine Parasites.com provides an interactive tool for scheduling re-dosing (without specifying dosage) based on temperature and salinity; but it makes no distinction of efficacy at different salinities. Regardless, I don't believe I am dealing with Neobenedenia. I have somewhat reluctantly already reduced specific gravity to 1.018 with the aim of continuing to decrease salinity, but only as low as you recommend. Is hyposalinity plus medication more effective, contraindicated, or inconsequential?

Question: What OTC fish anaesthetic is tang safe?

IMG_2461a.JPG DSC_0416a.JPG
 
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Looks like the Platyhelminthes known as Schistosoma fluke
PraziPro should beat this fluke
 
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Peter Houde

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Yikes! I hope I can't catch it. Snails could explain how this got introduced if they are intermediate hosts of marine schistosomes as they are of freshwater species. Some hitchhikers came in with some new macroalgae recently. The ID is good news I suppose if correct and that it can be reliably treated with prazi. Any thoughts about the efficacy of hyposalinity and its safety for my tank inhabitants?

It seems my tank image did not upload properly in my original post. I'm attaching it to this message for reference. It only shows the middle third of the aquarium but it is fairly representative of what is not visible except that rock/coral skeletons extend vertically nearly to water line to sides out of view.
 

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Peter Houde

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I wrote to various parasitologists and marine veterinarians in the United States, Brazil, Malaysia, Japan, and Australia who had published peer-reviewed studies on monogeneans. Most responded. I have it on good authority that my unknown pest is a ciliate protozoan, not a 'fluke' at all. I was surprised to learn that some of the many hundreds of thousands of different species of ciliates belonging to multiple Classes and even more Orders grow to as much as 4 mm long and are worm-like and active (e.g., Spirostomum). Some are parasitic, many are not. So far, there seems to be little possibility of positively identifying what is in my aquarium, so I don't even know for sure whether these are afflicting my tang or whether they are providing a food source for my mandarin - or both. One thing for sure is that the tang has the facial discoloration one might expect from HLLE as well as fin decay, so something is afflicting it. It's been one week on 2.5 mmg/l praziquantel so far, during which I did three small (5%) water changes with 5.0 mg/l praziquantel to account for degradation (see Thomas et al 2016 PerrJ, DOI 10.7717/peerj.1857). Salinity down to 22.6 ppt (1.017 SG) at 25 C. I've also treated daily frozen fish food with metronidazole, nitrofurantoin, and garlic extract for the past several weeks. The good news is that I haven't lost any tubeworms, snails, crabs, tunicates, copepods or amphipods. The bad news is that the tang hasn't gotten any better. I do hope to be able to trap him out and treat him with a copper-based medication, but that's not a solution for the display tank. I'm hoping Ruby Rally and Kick-Ich will put a dent in whatever may exist in the display tank without killing the good guys. I haven't started that treatment yet. This is proving to be an educational experience, one that is still far from over.
 

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I wrote to various parasitologists and marine veterinarians in the United States, Brazil, Malaysia, Japan, and Australia who had published peer-reviewed studies on monogeneans. Most responded. I have it on good authority that my unknown pest is a ciliate protozoan, not a 'fluke' at all. I was surprised to learn that some of the many hundreds of thousands of different species of ciliates belonging to multiple Classes and even more Orders grow to as much as 4 mm long and are worm-like and active (e.g., Spirostomum). Some are parasitic, many are not. So far, there seems to be little possibility of positively identifying what is in my aquarium, so I don't even know for sure whether these are afflicting my tang or whether they are providing a food source for my mandarin - or both. One thing for sure is that the tang has the facial discoloration one might expect from HLLE as well as fin decay, so something is afflicting it. It's been one week on 2.5 mmg/l praziquantel so far, during which I did three small (5%) water changes with 5.0 mg/l praziquantel to account for degradation (see Thomas et al 2016 PerrJ, DOI 10.7717/peerj.1857). Salinity down to 22.6 ppt (1.017 SG) at 25 C. I've also treated daily frozen fish food with metronidazole, nitrofurantoin, and garlic extract for the past several weeks. The good news is that I haven't lost any tubeworms, snails, crabs, tunicates, copepods or amphipods. The bad news is that the tang hasn't gotten any better. I do hope to be able to trap him out and treat him with a copper-based medication, but that's not a solution for the display tank. I'm hoping Ruby Rally and Kick-Ich will put a dent in whatever may exist in the display tank without killing the good guys. I haven't started that treatment yet. This is proving to be an educational experience, one that is still far from over.
Based on an initial glance, I was very suspicious that this was a Schistosoma. I am not an expert on the subject, but some basic research revealed several problems with that theory. Great job with the thorough research. Many times I have seen some reefers on this forum misidentify things. It is often better not to say anything than to give a wrong answer.

Regarding the kick ich, there is no compelling evidence imo that it does anything useful. It is really up to the manufacturer to provide evidence of it working, and the haven't.
 
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Peter Houde

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Based on an initial glance, I was very suspicious that this was a Schistosoma. I am not an expert on the subject, but some basic research revealed several problems with that theory. Great job with the thorough research. Many times I have seen some reefers on this forum misidentify things. It is often better not to say anything than to give a wrong answer.

Regarding the kick ich, there is no compelling evidence imo that it does anything useful. It is really up to the manufacturer to provide evidence of it working, and the haven't.
In case anyone is interested, I finally got the answer - and it is GOOD NEWS! They're not parasitic. Here's the letter I received this morning from the Institute of Parasitology (https://www.paru.cas.cz/en/sections/aquatic-parasitology/laboratory-of-fish-protistology/):

Dear Peter,

our colleague, Peter Vdacny, from University of Bratislava, Slovakia, determined this ciliate to family Pseudokeronopsidae, exact species determination is impossible without more details. Peter Vdacny, in his recent paper studied this group of protists.

(Tengyue Zhang, Yurui Wang, Ting Cheng, Jiyang Ma, Peter Vdacny, Weibo Song and Chen Shao. 2020. Systematics and Multi-Gene Phylogeny of the Subfamily Nothoholostichinae (Ciliophora, Hypotrichia), With Integrative Description of a New Marine Species Nothoholosticha luporinii n. sp. Frontiers in Marine Science. doi: 10.3389/fmars.2020.610886)

This group of ciliates is not parasitic one.

Best regards

Ivan
 

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Peter Houde

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I would greatly appreciate your advice regarding the identification of and treatment for a "fluke" that has recently infested my tank and Paracanthurus tang.

I have a marine aquarium that is heavily infested with some form of monogeneans. One fish exhibits overt disease ("blue tang", Acanthuridae: Paracanthurus hepatus; probable infestation of cornea, loss of color in facial region, deterioration of dorsal and caudal fins possibly due to secondary infection). Several other fish are seemingly unaffected (including 15-20 yr old clownfish), but a damselfish that permanently lost facial color many years ago may have been harboring parasites all along. It also has some tattering of pectoral and caudal fins, and both it and a mandarin have developed small (<1 mm) unequally sized white spots within the last days since I began treatment (described below). The tang's behavior is normal. It does "twitch" but this seems to be only in response to human proximity/close observation; it does not seem to twitch when observed from a distance and it does not rub or scratch itself on objects. None of the fish do. None of the fish show labored breathing. I am anxious to identify the parasite at least at a taxonomic level that will help me to decide the best method of treatment, both for the fish and the entire aquarium.

Tank: established >25 years; fish only; 473 liters; temperature 78F, 25.5C; specific gravity typically 1.024 (but currently 1.018, please see below); nitrate ca. 15 mg/l; no ammonia or nitrite test but pH 8.15 and NO3 suggest this isn't an issue; no copper test but no conceivable source of copper; phosphate ~0.32 (Hanna spec; lower by Salifert and Reef Master tests); KH/Alk 10.33-10.5 (Salifert; 9-10 by Reef Master); Ca 430 ppm (Salifert: 380 by Reef Master); Mg 1290; biological filtration (bio-balls in sump, 5-6 cm coral gravel, abundant purple coralline algae, and Gracilaria, Chaetomorpha, and Penicillus macros) and protein skimmer. I apologize the image of my aqarium is not a full view but it is representative of the whole tank.
Inhabitants: 2 Amphiprion ocellaris, 1 Chrysiptera parasema, 1 Pseudochromis paccagnellae, 1 Synchiropus splendidus, 1 Paracanthurus hepatus, various snails (cerithiids, Neritina, Nasarius, unidentified), emerald crabs, bristle worms, tube worms, unidentified worms, more bristle worms, unidentified colonial tunicates, unidentified encrusting sponges, amphipods, copepods, and things that mysteriously come and go as if by spontaneous generation - now to include monogeneans.

It is not practical for me to capture the afflicted tang (though I've not ruled out the possibility entirely), so I have not been able to examine adult parasites. I also have not observed eggs. However, oncomiracidia were suddenly frighteningly abundant on the aquarium glass. None can be found still 2 days after water change and glass cleaning, but I refuse to believe that they are not all over the live rock. I check the glass regularly for copepods and I've never seen oncomiracidia before. I recorded a video that is decidedly of better clarity than the attached still photo, but at 139 Mb the video is too large to upload. You can access it if you wish on my server at:

http://lithornis.nmsu.edu/~phoude/oncomiracidium 139 Mb.MOV

There are a few characteristics I can describe. It is at least somewhat shorter and much narrower than an adult copepod, e.g., Tisbe. It is ciliated on what I interpret as its dorsal side. There are very long and pronounced cilia around its anterior end that beat synchronously and continuously and extend deeply into its pharynx or caecum. The caudal-most cilia are also elongate. It has no eye spots and no anchor hooks that I can discern, so I do not believe this is Neobenedenia even if that is the most common scourge of marine aquaria. The oncomiracidia on the glass of the aquarium are considerably more elongate than the one in my image, and they are quite active. Under the microscope they become shorter in length and soon disintegrate, possibly killed by the focused microscope light.

Question: Can you identify this to a level that would assist in determining the best treatment?

Question: I dosed the tank once with praziquantel to a concentration of 2.5 mg/l (on 2021/02/27) given my crude estimate of tank water volume after displacement by gravel and live rock. I've been supplementing frozen food diet (San Fransisco mysis, brine shrimp, and Emerald Entree, and Ocean Nutrition Formula 2) with metronidazole (SeaChem Metroplex) and nitrofurantoin (SeaChem Focus) garlic extract and Brightwell's Aminomega daily for 3-4 weeks. I have read some conflicting information regarding the appropriate dosing of praziquantel that I hope you can arbitrate. Hikari's Prazipro recommends dosing of 2.5 mg/l with the potential for re-dosing in 5-7 days but as early as 3 days, and that seems to be the popular opinion. However, several published references suggest that 2.5 mg/l should be added every 2 days until 10 mg/l is reached. I'd appreciate advice on protocol or alternative treatments.

Question: Reefs.com (Joe Rowlett) advocates reducing salinity to 15 ppt for 5 days (specific gravity 1.011), citing several studies on its effectiveness for treating for Neobenedenia. One of those references specifically found 18 ppt (SG 1.013) ineffective. That frightens me. Is 15 ppt safe for fish? Is it safe for snails, crabs, coralline algae, copepods, etc? (no live corals) Marine Parasites.com provides an interactive tool for scheduling re-dosing (without specifying dosage) based on temperature and salinity; but it makes no distinction of efficacy at different salinities. Regardless, I don't believe I am dealing with Neobenedenia. I have somewhat reluctantly already reduced specific gravity to 1.018 with the aim of continuing to decrease salinity, but only as low as you recommend. Is hyposalinity plus medication more effective, contraindicated, or inconsequential?

Question: What OTC fish anaesthetic is tang safe?

IMG_2461a.JPG DSC_0416a.JPG
For anyone interested, these turned out not to be flukes at all; rather, non-parasitic giant worm-like protozoans (see thread below). And like so many other things, they eventually disappeared as mysteriously as they arrived.
 

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Hello Peter, Would it be possible for you to share the link to your video in your first post again?
I am interested in comparing this with what we currently have inhabiting the glass in our tank. A few of our fish have started exhibiting signs of what could possibly be flukes.
We are currently setting up a separate QT for one of our larger fish that's a bit older and has already been through a lot. For 'her' sake we are only trying to boost immunity through healthy nutrient rich food (everyone is still eating as usual) until the QT is fully set up and prepared with, hopefully, the best suited treatment method.
Thank you in advance.
 
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Peter Houde

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Hello Peter, Would it be possible for you to share the link to your video in your first post again?
I am interested in comparing this with what we currently have inhabiting the glass in our tank. A few of our fish have started exhibiting signs of what could possibly be flukes.
We are currently setting up a separate QT for one of our larger fish that's a bit older and has already been through a lot. For 'her' sake we are only trying to boost immunity through healthy nutrient rich food (everyone is still eating as usual) until the QT is fully set up and prepared with, hopefully, the best suited treatment method.
Thank you in advance.
Sure, here are links to videos of them on the aquarium glass where they appeared worm-like and very active and under a compound microscope where they sucked up into a more globular shape whether because of the heat of the light or pressure of the coverslip. Bear in mind though, that they turned out to be non-parasitic protozoans rather than 'flukes', despite their size and worm-like appearance. I suspect they were hitchhikers on some macroalgae I'd bought. They eventually disappeared all on their own just as mysteriously as they appeared. That seems to happen all the time year after year with one new thing after another. It always keeps things "interesting". Incidentally, whatever was causing the HLLE symptoms in my tang and damsel, the damsel was cured (!) after treatment with enrofloxacin. It's miraculous considering the guy had been afflicted for ~10 years. I keep hoping the tang will improve, but only time will tell.


Cheers, Peter
 
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PurpNurp

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Thank you! We have a large Blue Hippo, a very large Male Blonde Naso Tang (Who has barely eaten since we got him.) We always have the LFS feed before we take anything home and they had him for about a month in a tank by himself..
We also have a large Desjardini Sailfin and a Red Sea Purple Tang. The only one that is exhibiting signs of deteriorating is our Blue Hippo.. She has gone through 2 horrible experiences of Marine Velvet and has somehow made it... I will do everything in my power to save her (and of course all the other fish)..
Thank you again Peter!
 
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Peter Houde

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Thank you! We have a large Blue Hippo, a very large Male Blonde Naso Tang (Who has barely eaten since we got him.) We always have the LFS feed before we take anything home and they had him for about a month in a tank by himself..
We also have a large Desjardini Sailfin and a Red Sea Purple Tang. The only one that is exhibiting signs of deteriorating is our Blue Hippo.. She has gone through 2 horrible experiences of Marine Velvet and has somehow made it... I will do everything in my power to save her (and of course all the other fish)..
Thank you again Peter!
Wow, that's a lot of big tangs! You must have a really big aquarium. I was sorely tempted to get a Desjardini but I eventually decided my 125 gallon just wouldn't cut it in the long run. Unfortunately the same for a lot of other really striking fish.

The blue Paracanthurus are really the oddballs among tangs, it seems. Not surprising since they're a monotypic genus in the family. I had one that was healthy as could be for many years but it never grew to be large. Some years later I added 5 more fairly small ones that were fantastic. They were healthy and beautiful and schooled about in perfect unison. Then, one by one, they disappeared. I think the original, who was larger and only occasionally schooled with them, killed and maybe even ate them. I never found a trace. Somewhere down the road I added a fish that had what looked like HLLE. Whatever it had was contagious and several of my older and favorite fish died. Some others, even some of the same species that died, survived for 10-15 years longer, albeit with the same HLLE-like symptoms. I waited years in hopes that all of those fish would eventually die off so I could start from scratch, but it eventually became clear that two humongous old clowns that never showed symptoms and the damsel I wrote about above in this thread that did (completely unpigmented face) would probably outlive me. I got impatient and bought a new Paracanthurus just this year and of course it contracted the disease immediately. You can imagine my surprise that the damsel completely recovered after ~15 years but the tang did not (at least not yet) after I treated them both with enrofloxacin. Just two weeks ago I added a powder brown tang (and one spot foxface) to the aquarium. So far it looks great, and has a much more outgoing personality than the blue. The most wonderful thing is that the two newest fish have really encouraged the Paracanthurus and even the clowns to come out and be much more conspicuous. And the Paracanthurus even learned from the others to eat nori from a clip, something I'd been unsuccessfully trying to get it to do ever since I first got it. It's all great.
Cheers, Peter
 

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We have a Red Sea 3xl 900- it was quite interesting to set up when it finally arrived.
And yes ours is very much so an oddball. Pretends to act tough with the other tangs but will "throw fits" when we add any new corals to the tank.. She will put her back end to our hand and try to fight us like we are another tang.. Then just swim off into the rocks and poke her head out to watch us.
We have done a dip on her to help provide a bit of relief until the medication starts to take effect.. I hope she gets better soon. Our hippo is about 7in. The Desjardini is slightly larger than the Hippo and he is quite the character. He has been acclimated to tank life for many years and will follow you up and down the tank to get your attention. He even recognizes that bag we keep their nori in. When he sees it he starts going crazy and does a little dance / skip up and down the tank glass.
 

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