Does my Derasa has PMD?

[hsp]

I read a lot about clams, including James Fatherree's book. I think that PMD means that there is gap between the mantle and the shell, but I am not sure if this is always the case. My Derasa grew for months and looked fine; suddenly, part of the mantle is retracted but still fully attached. Shall I do a FWD for 30 min just to be sure?

 

[Mr. Mojo Rising]

This clam has not been growing for some time, there is no new white growth at the top of the shell. This is the most important thing to watch for when owning clams.

Seeing the clam beside zoa's, I would guess it is not getting enough light.

I would not freshwater dip the clam, this clam might not be healthy enough to survive IMO. Personally I would give it more light and double check the parameters. Good luck

 

[twentyleagues]

I dont know about pmd in this case but it for sure isnt healthy. As @Mr. Mojo Rising said possibly lighting, any idea the par value where it is? Derasa dont need as much light as some other clams but they still need decent amount more than zoas need to survive.

 

[minus9]

As mentioned above, this is starvation and a FW dip would only stress the clam more. You can increase the lighting, but from the looks of it, I don't think it will survive for very long. Any new additions (other clams) recently? Unstable parameters and not enough light are usually the case with these symptoms.
Did the clam attach itself to the cradle? For derasa, I would put the clam on the sand and provide enough light in that area for the clam, as they don't stay attach forever.

 

[hsp]

I should have given a bit more context:
- I bought the clam in October 2024 from a fellow reefer who shut down his tank. He had several clams. This Desara was in the cradle (but not attached) on the sand bed.
- It attached to the cradle in my tank and grew significantly--see image from January 2025 below--all the new white was during my time.
- Light: I have a Red Sea Reefer Max G2+ 300 with 2 ReefLED 90. According to the specs, this would give ~380 par at the 23 cm (9 in) depth where the clam is located at 100% intensity. But I run between 70% ramping up to 90%--see the program below for white, blue and moon.
- I do not target feed the clam but dose 20 times a day Phyto with BBS for a total of 200 ml per day for my 80-gallon (300 l) system.
- My other filter feeder is a Crinoid (feather stars), which is growing well.
- Last water test: Salinity: 35; pH: 8.7; Nitrate: 11.8; Phosphate: 0.20; Alk: 10.3; Mg: 1440; Ca: 470; Ammonia: 0.11 (pretty stable with the Phosphates sometimes going to 0.15 and Nitrates going as high as 18)

Any other suggestions? Thanks in advance for your help!

 

[Tahoe61]

Are you running GFO or similar products? Is that the only clam?

 

[minus9]

So from January until now, when did you notice a decline in growth? Also, what fish do you have in the tank?

 

[minus9]

Also, without measuring the light intensity, a program means nothing, especially numbers coming from the manufacturer, which are always overrated/inflated. Actual numbers where the clam resides would be the only reliable measure if the clam is getting adequate lighting.

 

[hsp]

Are you running GFO or similar products? Is that the only clam?

No GFO. This is the only clam.

 

[minus9]

It usually takes clams weeks if not months for starvation to take its toll, but the lack of growth would be obvious only after a week or two. But if this is your first clam, then the signs might not be so obvious or recognizable. The upper margins turn dark as they get covered in algae and the white rim reduces quite a bit. The clam will reduce in reactivity to light changes as it gets weaker, then it can barely close. Once it can no longer close fully, it’s just a matter of days, if not hours until it succumbs.

 

[Uncle99]

Mine does that from time to time when “bothered” by someone. It sometimes takes a day or two to spread back out fully.

Until then, I’d make no change at all.

It looks quite healthy to me.

 

[hsp]

Mine does that from time to time when “bothered” by someone. It sometimes takes a day or two to spread back out fully.

Until then, I’d make no change at all.

It looks quite healthy to me.

Thanks a ton!

 

[hsp]

So from January until now, when did you notice a decline in growth? Also, what fish do you have in the tank?

I think there was a decline in growth for the last 2-4 weeks. Hard to tell.

Fish, Inverts:

• 1 x Male Lyretail Anthias
• 3 x Female Lyretail Anthias
• 1 x Bicolor Blenny
• 2 x Orange Ocellaris Clownfish
• 1 x Pajama Cardinalfish
• 1 x Bristletooth Tang
• 1 x Yellow Wrasse
• 1 x Bicolour Dottyback, Pseudochromis Paccagnellae
• 1 x Shortspine Urchin
• 1 x Tuxedo Urchin
• 2 x Coral Banded Shrimp (Stenopus hispidus)
• 5 Peppermint Shrimp
• 1 x Banded serpent starfish (Ophiolepis superb)
• Astrea Turbo Snails
• Nassarius Snails
• Trochus Snails
• Strombus Snails
• 1 x Gold Ring Cowrie
• Cerith Snails

 

[dansyr]

I should have given a bit more context:
- I bought the clam in October 2024 from a fellow reefer who shut down his tank. He had several clams. This Desara was in the cradle (but not attached) on the sand bed.
- It attached to the cradle in my tank and grew significantly--see image from January 2025 below--all the new white was during my time.
- Light: I have a Red Sea Reefer Max G2+ 300 with 2 ReefLED 90. According to the specs, this would give ~380 par at the 23 cm (9 in) depth where the clam is located at 100% intensity. But I run between 70% ramping up to 90%--see the program below for white, blue and moon.
- I do not target feed the clam but dose 20 times a day Phyto with BBS for a total of 200 ml per day for my 80-gallon (300 l) system.
- My other filter feeder is a Crinoid (feather stars), which is growing well.
- Last water test: Salinity: 35; pH: 8.7; Nitrate: 11.8; Phosphate: 0.20; Alk: 10.3; Mg: 1440; Ca: 470; Ammonia: 0.11 (pretty stable with the Phosphates sometimes going to 0.15 and Nitrates going as high as 18)

Any other suggestions? Thanks in advance for your help!

Chemistry looks pretty good but pH 8.7 strikes me as a bit high, testing issue or is it really running that high? Not that it's necessarily bad, but my eyebrows are raised. I run pretty NSW levels of ~6-8 dkh alkalinity and pH 8-8.2.

Also that "before" shot doesn't look super great to me - good mantle extension but it looks pretty translucent to me. When fully extended you can usually end up seeing some extra-dark patch where the shell is, but that's a little more translucent. Suggests to me it might not be photosynthesizing too well then, which could explain why growth stalled - if it had low zoox density for whatever reason, be it shock, light, pathogen, whatever, so it was growing on reserves but those run out eventually and here we are.

Other guess could be directional - from angle of photos, is it close to a wall (that might be shading)? or getting blasted by flow on that side? Sometimes mine gets moved closer to walls or rock face and gets less light until I notice and scootch it back.

If you don't have access to a buddy with a PAR sensor, consider getting a cheap LED floodlight and putting it over for a week or two, and see if it improves.

 

[hsp]

Thanks, everyone, for the input! I wanted to close the loop on this one: I did two things (yes, I know one should only do one at the time to see what makes a difference):

• I put a PVC pipe into the tank installed vertically (temporarily). I placed the cradle with the attached clam on it to position it about 10 cm below the surface and directly under a ReefLED 90, which provides plenty of light running at ~90% for ~10 hours.
• I added a GFO/Carbon Media Reactor (https://reefpurero.com.au/product/gfo-carbon-media-reactor/) which came with a Sicce Syncra Silent Pump 1.0 - 950l/h: added Blue Life Phosphate Fx ~100 ml (https://www.aquaristiconline.com.au/products/blueliferegenerableresinsphosphatefx500ml) and Activated Carbon. The pump running at full power but flow is slow due to the packed media. This brought the Phosphate slowly down 0.1 ppm.

Here the pictures from yesterday. I am by no means an expert but I think the mantle looks more extended a slight white line is again visible. What do you think?

 

[Tahoe61]

Why don't you perform a 30 min freshwater bath?

 

[dansyr]

That growth looks great! That's a really cool mantle pattern too, I don't remember seeing many derasas with the spots like that

 

[minus9]

You have some new growth, that's a good step in the right direction. I would also keep an eye on that blenny, they are known nippers of clam mantles (not saying it will, but the potential is there). I would raise the intensity of your light by 5% more or extend the peak period by an hour or two to help. Remember, intensity and duration work together. So if you're maxed out on intensity, extend the time slightly to help out.

 

[hsp]

Why don't you perform a 30 min freshwater bath?

Someone in this thread doubted that it is PMD and that it would stress the clam too much. What do you think? Can't-hurt approach?

 

[hsp]

You have some new growth, that's a good step in the right direction. I would also keep an eye on that blenny, they are known nippers of clam mantles (not saying it will, but the potential is there). I would raise the intensity of your light by 5% more or extend the peak period by an hour or two to help. Remember, intensity and duration work together. So if you're maxed out on intensity, extend the time slightly to help out.

I will try that. Thanks!!!!