Does my clam have PMD?

[xjiang7]

I have this clam for over two years now. It has been healthy and growing.
About one month ago I moved and upgraded into a 70 G tank. Two days ago I found that my clam began gaping during the night.
I took it out and inspected closely, and did not find sign of parasitic snails.
Here are some photos this morning. Is it have the pinched mantle disease?

 

[mystersyster]

My derasa clams do this every now and again. I'm not sure if it's PMD but I'd put some fresh carbon in the tank if you haven't already. Clam looks healthy to mw though.

 

[xjiang7]

My derasa clams do this every now and again. I'm not sure if it's PMD but I'd put some fresh carbon in the tank if you haven't already. Clam looks healthy to mw though.

Thanks for the suggestion. I am suspecting that as it has shown signs of stress recently compares to the way it used to be.
Here is a photo I took this April in the old tank

 

[xjiang7]

It gaps widely in the evening : (