Think I found my answer

[Huskymaniac]

So here is what it looks like now. Seems to be expanding the mantle but its curling in the front. Never seen that before.

 

[ocboat]

Is looking better, don't give up. I have a derasa that I was sure wasn't going to make it after a dosing issue. It looked similar to yours but after I fixed the issue, it slowly returned to normal. I too lost my entire collection a couple of years ago from some type of infection from a 1.5" ORA maxima. After several attempts to keep one alive, I found a supplier that my LFS uses and have been able to keep a few alive for several months now.

 

[Huskymaniac]

Here we are today. Looking a tad bit better. Still gapping at the mouth though.

 

[Shigshwa]

Looks to be pulling out! I think time is gonna put this guy back to normal now.

 

[Huskymaniac]

Here is an updated photo of the clam. Still gaping at the mouth and the mantle is a little squared off at the end which I think has to do with the gaping mouth. The clam is pretty much open all the time and is very responsive to light and shadows. Hoping we are on the road to recovery and the gaping goes away. Tomorrow I will be doing a 25% wc and replenishing carbon. Today is day 4 after the freshwater dip.

 

[LadyMac]

Nice! Hope the guy pulls through, he’s quite adorable, as clams go

 

[DSC reef]

Looking better. Typically when the incurrent siphon is open like that the clam is taking in water so it's not a bad sign. Gaping is when the mantle starts retracting into the shell to where you can see white inside the shell. I think your clam is making great progress.

 

[Huskymaniac]

Here is how we are looking today. Did a water change last night and mantle extension is looking better. Still dealing with this wide open gaped mouth. Today is the 6th day after the f/w dip.

 

[Paul B]

Looks happy as a clam to me.

 

[Pife]

How's it doing?

 

[IronChefItaly]

I've had a few scares with my clams. My derasa had great growth over 3+ months then suddenly was showing signs of pinched mantle. After the 3rd day of decline I decided to dip it in freshwater because I didn't think it was going to rebound on its own. It looked very similar to yours, gaping mouth, withdrawing mantle and after about 6-7 days it was fully recovered. In months following, I watched it like a hawk and there were two more periods of sudden pinched mantle. I catch it one day and wait for it to be there 24 hours later then follow with a dip - no more messing around. Three dips over 6 months and I've been in the clear for over a year now. I've heard awful experiences from Divers Den specifically regarding clams. I honestly wouldn't buy one from there without quarantining it. I came across one thread where a fellow had the most beautiful collection of clams I've ever seen in one place. He bought another clam from Divers Den and soon after he lost all of his clams. The before and after picture was awful. Would like to hear if your clam made it, apart from the gaping exhaling siphon it looks to be recovering nicely.