Diagnosis and Treatment of Pinched Mantle Disease in Giant Clams


It was almost 20 years ago when I first introduced the Fresh Water Dip (FWD) protocol for the treatment of Pinched Mantle Disease (PMD). Over the years, many reefers altered the protocol somewhat but, on the whole, it still is the only tried and true way to treat PMD, a universally fatal disease if untreated. FWD is effective for PMD as described below. However, it is not the treatment of all clams that do not look well. It is very important that the diagnosis is correct in order for us to effectively treat diseased clams. There are likely many different diseases that cause clams illness, PMD is only one of these diseases.
I am an avid aquarist. I have been keeping fresh water aquarium since I was a child. I started my first marine aquarium in 1980 and reef aquarium in 1996. I also got hooked on clams in 1996. Those days, one can only get Ultra Blue Maxima from the Red Sea, and they were expensive. In 1997, I ordered several Crocea, Maxima and Squamosa clams from Dick Perrin at Tropicorium in Romulus, Michigan. This shipment was delayed by UPS for 1 day. When the shipment did not arrive, I called Dick to check the status of the order. He reassured me that the clams would be fine. Dick said the clams were healthy and he packed them well. He also said the clams were hardy enough to tolerate the delay. As example of how hardy clams are, Dick mentioned that he once forgot a tray of Maxima clams for several hours in fresh water. The clams tolerated the mishap fine, none of them died. On further discussion, Dick said all his newly imported clams received a fresh water dip for disease control. This planted the seed of using fresh water dip as a possible treatment for clams in my head. Dick was right about the clam shipment. All my clams arrived in good condition. Enclosed are some pictures of the clams I got from Dick Perrin back in 1997. These pictures are of poor quality because digital cameras at the time were expensive and of very low resolution. Even with these poor resolution pictures, we all can see that these clams are healthy and very colorful. These were the Ultra Maxima and Crocea back then. I am not sure why but these Ultra Crocea are not available very often today. Below are the clams I ordered from Dick Perrin at Tropicorium.
Ultra Blue Maxima, the absolute most expensive clam I owned back then.

Beautiful Ultra Crocea. My tank was fully hooded with light on the hood so taken top down picture was not possible. I wish I have image of these clams top down.

A few years later, back in 2001, I was a clam fanatic and had a large number of Tridacna clams of all 5 known species, at the time. PMD was also started to become very common back then. I wrote about this in an article archived on Reef2Reef article library, linked below. Needless to say, I was up to my eyeball with PMD
With observation and experimentation, I was able to overcome and cured my clams, eliminated PMD from my tank. In this thread, I hope to impart these hard won knowledge hoping to help some of my fellow reefers, and help keep these jewels of the Ocean well care for in our tank.

What is Pinched Mantle Disease?
PMD is only one of the various causes of clam mantle retraction. I struggled with this so much. I can clearly remember the disease and can still even visualize the image of some of my clams. These are pictures of my clams in 2001. You can find these pictures in the Inaugural Issue of Advanced Aquatist, an online reef publication started on January 2002. Link to the January 2002 issue and another link to the aquarium album are attached below.
These are some pictures from the album above showing my clam with this unknown disease, unknown at the time. Still these clams are healthy enough, even as I and my clams struggled with PMD.

Four of the five species of Trinacda represented here. Of these, the Squamosa, incidentally the same Squamosa I had since 1997 was the sickest. About 1/2 of one side of his mantle was retracted. The three Maxima's were also affected. Only the very tip of the Derasa was affected and the Green Crocea's disease was not apparent in this picture.

Close-up picture, the disease of my two favorite clams can be easily seen.

The Gigas I raised from about 1.5 inch size and moved across the country to Corpus Christi from Seattle, sicken but not apparent here. The Ultra Crocea also sicken with the top part of the mantle retracted.

I struggled with this disease for several years. These were my observation of Pinched Mantle Disease:
  • The previously healthy clam, newly infected will appears healthy but will have retraction of one area of the mantle. This was not true with clam that was send to me sick, but always true with clams that were healthy then infected in my tank.
  • The irritated, diseased mantle always retracted at the same place and mantle retraction spread from there.
  • This disease affected all five species of Tridacna in my tank.
  • The disease was slow in onset and healthy clams can live for months with this disease. My large Gigas live for over 1 year with the disease until I cure him with FWD
  • Clam mantle retraction spreads slowly from one area to adjacent area, rarely skipped area of mantles.
  • Disease spread from adjacent clams most easy but there are infections of clams at distance location. This is much more common when the numbers of clams that were infected in a tank increased.
  • Clams look better in AM, but mantles become much more irritated, more contracted by the end of the photoperiod.
  • As the days go on clams secrete strands of mucus that can be seen extended from the disease mantles
  • As the disease progress, the mantle retraction worsens and the diseased clam dies of starvation.
I read the article “The Pinched Mantle Syndrome in Giant Clams” by Dr. David Basti, Deborah Bouchard and Barry Neigut in Conscientious Aquarist Magazine which has the following abstract:

Pinched Mantle Syndrome is a term used by marine reef hobbyists to describe a disease condition in the ornamental clam Tridacna crocea and Tridacna maxima. The disease causes localized mantle retraction, gaping, loss of coloration and, eventually, mortality. A Perkinsus olseni-like protozoan has been identified as a possible cause of the disease. Based on this preliminary work, histopathology is the preferred method to confirm the presence of the parasite within the tissue of Tridacna crocea.”

I just wanted to say that this does not describe the same disease. The authors were looking for pathogen within the tissue of the clams, disease within the tissue will never response to a fresh water dip. Because of this reason, it is likely that the parasite within the tissue of some of the clams by these authors, while can cause clam illness, was not true pathogen for PMD as described above, and effectively treated with FWD

How to Fresh Water Dip our diseased clams?
FWD for 30 minutes and transfer to a new tank, free of PMD, is effective in the treatment for PMD. Fresh water need to be brought up to around tank temperature. I did this by but the water in milk plastic container and drop it into the sump for at least 15 minutes until needed. Place the water in a suitable container and place the clam in it for 30 minutes. Aeration is not needed. I used RO water use but essentially any fresh water without chlorine or toxin will do. Once, I advise the owner of Fishland, a LFS in Houston, on treatment of his PMD infected clam. Andy just put his sick clam from the reef aquarium to one of his fresh water aquarium for 30 minutes and then moves him to another reef aquarium. This cure the clam and he sold this beautiful Ultra Maxima, later that week, healthy and disease free.
I do have a word of caution regarding using FWD to treat PMD in clams. This treatment will only work if the disease is diagnosed correctly and the clam is still strong enough to tolerate treatment. PMD kills slowly. The parasite load increase, and cover more of the mantel causing irritation to the mantel of the clam resulting in contraction, thus starving of the clam. Anything that irritates the mantle will result in retraction. Therefore, just because the mantle is retracted does not automatically mean that the clam has PMD. FWD is still the only treatment for PMD that is effective.
The clam need to be place in a tank that is free of PMD in order for treatment to be most effective. However, from observation, I can deduce that the pathogen of this disease is an obligate parasite and cannot live for long without the host. Back in 2002, my Gigas was about 16 inches, I was not able to have a disease free tank for him. I moved all my clams to one side of my 8 foot tank for a few days, then I treated all my clams at once and place them back on the other side of the tank. This step cure my tank of the disease.
Below are pictures of a Derasa of a friend, Outerbank a member here on Reef2Reef, with PMD. He treated this clam with a 30 minute FWD as per my recommendation and was able to cure it. Pre and post treatment of this beautiful Derasa clam is attached below.

Pre Treatment. Part of the mantle is retracted, can easily seen.

Another view of the same clam

Post treatment. Outerbank, a few weeks post treatment here:

Same clam, 6 weeks post treatment.

Why and how fresh water dip works (in PMD)?

Fresh water is toxic to marine animal. It is toxic because if we put any living tissue that normally lives in sea water into fresh water, the osmotic changes will result in the cell absorbing water, swelling up and rupture. Animals with exoskeleton likely tolerate this a little better than soft body animals. Also the larger the animal, the longer they can tolerate fresh water dips. This is due to the fact that larger animals have a smaller surface to volume ratio than smaller animals. This is why parasites, smaller animals (maybe single cell organism) normally die much quicker in fresh water immersion than the clam. Also the parasite must be on the surface of the infected animal. If the parasite is inside the tissue of the infected animal, the parasite will not be exposed to the fresh water, thus treatment will be ineffective. IMO, in PMD and ECS, the pathogens are small, maybe unicellular organisms, which lived on the surface of the host. Dipping the host animals in fresh water will result in rupture of the pathogens. If we remove the host animals from fresh water before they become irreversibly damage, they will recover and live on free of the pathogen.

What other diseases can we use FWD to treat?
Essentially any pathogens that infect the surface of a host can be treated with FWD. The therapeutic to toxic ratio of this treatment depends on how long the host can survive without permanent damage. This depends on the surface to volume ration of the host. The larger the host, on the whole, the longer they can withstand fresh water dip. By size I mean the total soft tissue mass. The size of a large SPS does not count. SPS have a very thin tissue layer over the skeleton, and con only tolerate water dips a few minutes, or less, only.
Most of us know that Elegance Corals sometime get sick with Elegance Coral Syndrome (ECS). This disease is very similar to PMD of clams in that the coral initially retracts on part of the oral plate and tentacles. This worsens with light exposure, and gets worst later in the day. The coral produces copious mucus. The retraction slowly spreads and the coral usually ends up fully retracted until it melt away leaving the skeleton. As far as I know, there is no treatment, and it is also a communicable disease. Introduce one sick Elegance Coral to a tank with healthy specimen will invariably result in death of both. I have been thinking about this treatment but I haven’t been able to experiment with it until a few weeks ago. One of my friends, Alton also a member here on Reef2Reef, bought an Elegance coral that ended up with ECS. As a last ditch effort to keep this coral alive, I recommended 15 minutes FWD. Alton’s Elegance did great and is on its way to recovered fully. I advised Alton to use 15 minutes FWD only for his Elegance coral since the soft tissue layer of Elegance coral is fragile and thin in comparison to clams. Pre and post treatment of this Elegance coral attached below.

Pre treatment
2019Elegance Pre treatmentresized.jpg

Post treatment for a few weeks. Well on his way to full recovery
Elegance Post treatment.jpg

We have always known that FWD can be used on fish for external gill parasites, LPS and SPS for various parasites like flatworms. To treat flat worms on corals, SPS and LPS swirl the coral in fresh water for several minutes, and blow the flat worms off of the corals. I have treated Euphyllia, Gonipora, and Alveopora with fresh water dip to remove parasitic flat worms from the coral successfully before. If the infestation is on the surface, and the coral or fish can tolerate fresh water for some duration of time, we can use it to kill, or at least disable the parasites and they will fall off of the hosts. If the host, invertebrates or fish, can survive the treatment, we can cure them of the disease by remove all the parasites with FWD.

I hope this write up will help some of the animals that we keep in our tanks. I would love to discuss FWD in disease treatment for our animals. I would like for reefers who try this treatment document the pre-treatment conditions and results. I would love to have more information and treatment results of FWD for ECS.
A few parting words, as with any disease, correct diagnosis is a must in order for the treatment to help. FWD treatment is toxic to the hosts, but nothing they cannot withstand if they are in reasonable shape. Because of this reason, once you determine that the diagnosis is correct, the earlier the treatment, the better the result. Waiting just weaken the hosts make them much less likely to tolerate treatment well.
Also, I would love to invite some researchers who have the mean, consider isolate and ID the pathogens that cause these two diseases. Looking at the right place, the surface of the host. I am sure it would not be difficult to ID these pathogen. I discussed this diseased with Barry, the owner of Clams Direct, and donated money to his effort to ID the organism. I wish I was able to give Barry and the researchers my view and what I know, at the time, regarding this disease.

Happy Reefing everybody.
About author
Reefer in Corpus Christi, Texas
Keep aquarium all my life, marine aquariums since 1980 and reef aquariums since 1996.
Passionate about Clams, Anemones and clown fish, Tangs, Angels and Wrasses

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Amazing information very well written and tons of helpful information :)
Very nice article...well done!
Very informative article on pinched mantle disease. I escpecially liked the photos that helped to illustrate the disease for people who have never seen it firsthand.
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