Derasa clam with Pinched Mantle Disease (PMD)?

[ncfalco]

Hello fellow reefers, I've had this 2.5 inch Derasa Tridacna clam for about a week now, and it hasn't been fully extending its mantle. It extended its mantle more fully on the first day that I added it to the tank. I drip acclimated the clam for one hour and carefully matched both the temperature and alkalinity of the shipping water to my tank. My parameters are as follows, all tested with Salifert kits:

Nitrate: 5-10ppm
Phosphate: 0.03
Magnesium: 320 ppm
Calcium: 450 ppm
Alkalinity: 8.3 DKH
Salinity: 1.026
Temperature: 78F

I'm currently running an 11 hour light cycle with my primary light source being a Red Sea 160s peaking at 100% intensity over a 45 JBJ AIO tank that has been running for about 1 year. The clam is responsive to changes in light and has attached its byssal threads to the rock clam hammock that I have it on. I've noticed a slight change in color on the clam, with purple hues changing to a more electric blue coloration under my lighting (hard to get a good picture of it).

I've observed some fish, in particularly my Tomini tang and lawnmower blenny, taking some nips at the algae on the side of it's shell from time to time, but only on rare occasions throughout the day. There is also noticeable white growth on the shell from the vendor. I've also observed the clam periodically going to the bathroom, which in my mind indicates that it is expelling excess zooxanthellae and getting enough light.

Do you think this could be pinched mantle disease (PMD) and that I should do a freshwater dip? Or is the clam likely still acclimating to my tank?

 

[Miami Reef]

which in my mind indicates that it is expelling excess zooxanthellae and getting enough light.

Correct. The brown stringy zooxanthellae is a very good sign.

The parameters look really good. The lighting is great. I wouldn’t be concerned about the fish picking the algae on the shell at all. The clam is retracted in the picture, but I don’t see any sign of PMD.

Does the clam ever fully extend the mantle?

 

[ncfalco]

Thanks @Miami Reef, I've read some of your other posts and you always provide helpful input. I also bought and read James Fatherree's giant clam book.

The clam will extend its mantle slightly over the edge of the shell, but it hasn't extended fully after the first day of being in my tank.

I've noticed some white/transparent stringy 0.5 cm strands of algae/bacteria on on the very edge of its shell where the mantle would normally cover. But I can't say if it's harmful or not. I've been very hesitant to try and brush the clam and stress it further.

 

[Miami Reef]

There’s no harm in removing the clam to scrub it, but I don’t think I’d waste my energy doing so. I don’t think it’s causing the retraction.

I think the clam is adjusting. Does it seem to extend more as the days progress? I think I’d reassess after a week. Everything seems great in your tank.

 

[ncfalco]

@Miami Reef It haven't noticed any additional mantle extension; It seems to be pretty consistent from day to day. One thing I have noticed is that it has tightly clinched its inhalant siphon shut. It will rarely open it for a brief period of time to pull in some water, but 99% of the time it is tightly shut.

Everything else in my tank seems very happy with excellent polyp extension, besides a single leptastrea frag that hasn't looked well for months.

 

[Miami Reef]

I think I’d wait a week longer. If it doesn‘t extend further, I’d consider moving it to a place with a bit more shade.

 

[Miami Reef]

Try putting the clam here. I think it might like it there a bit more. If it adjusts more, you can consider putting it back to the original spot.

 

[ncfalco]

Thanks again @Miami Reef. I'll consider reorienting things so I can move the clam to a slightly lower light area if it doesn't extend its mantle more this week. It's currently attached to a rather large "clam rock", so my options are a little limited in this smaller tank.

I'll provide updates and let you know how it goes!

 

[Miami Reef]

You’re very welcome. I think the clam will eventually fully extend in its current spot.

Keep me posted.

Your tank looks great!

 

[ncfalco]

Unfortunately I woke up this morning to a gaping dead Derasa clam. May consider trying again in the future, but haven't had much success with these guys. Perhaps I need to try a different supplier.

@Miami Reef Do you have any suggestions for the future?

 

[Miami Reef]

Unfortunately I woke up this morning to a gaping dead Derasa clam. May consider trying again in the future, but haven't had much success with these guys. Perhaps I need to try a different supplier.

@Miami Reef Do you have any suggestions for the future?

I’m sorry.

Purchase a clam that has its mantle fully extending at the LFS with new shell growth. Try opting for slightly less light until it seems like the clam is extending and clearly show signs of wanting more.

Check for pest pyramidal snails near the foot.

 

[exnisstech]

Sorry for the loss. I could never keep a clam alive until I bought a par meter and found out I was light starving them. My derasa is under 300 par and my maxima close to 400. But I doubt lighting is the cause of your clams death as it can take months for a clam to starve to death. Most likely it was already in poor health when you received it. On a side note everything I've read say derasa should be kept on the sand vs rock. My maxima is on rock but my derasa is on the sand. The derasa actually moves around some from time to time.
Derasa are pretty common in most LFS. As suggested look for the bright white new growth and full mantle extention. Also most clams will retract quickly when the light is blocked by passing your hand between the light and the clam. This is a good way to help check if they are healthy enough to quickly close. It's not full proof tho as some clams get used to fish blocking the light when they swim overhead and stop retracting when its blocked.
If by chance you can not find one local @PacificEastAquaculture usually has some nice clams. I have no affiliation but I did get my maxima from them 9-10 months ago and it has done well.

 

[Rugops]

If you have a decent petco nearby, you may find a derasa from time to time. A gold one is 30.00 around here.

 

[minus9]

Sorry I missed this, but it looks like the clam wasn’t growing at all. It’s hard to tell from the blue pics, but there’s no new shell growth and with derasa’s at this size, there should be a pretty good amount of new shell growth.