Great thread guys! I've read a lot of pinching threads in the past couple years but never once was the focus on finding out the cause.
First, I would like to say that, NO, I can guarantee that this protozoan is not species specific. I've been dealing with the pinching for close to 2 years now. I've had it on croceas, maximas, squamosas, and derasas. AFAIK, Minh Nguyen was the first to come up with the freshwater dip and tried it out for the first time on a large gigas just under 2 years ago. So that also confirms that it also affects gigas. The only clam that I've owned that didn't seem to have it was a Hippopus. Gee, I wonder why.:lol: Probably because its mantle doesn't extend over its shell.
I started out with 30 minute dips in RO/DI water that was aerated and the temp and ph was matched. As stated in this thread, the pinching always came back. I bumped the time up to 45 and still the pinching came back. It got to the point where removing all 15 clams to FW dip them became a bi-weekly "routine". There was one time where I forgot to set the timer and left the room to do a few things and completely forgot about the clams in the dip. I can't say for certain how long the dip lasted but it was for sure longer than 60 minutes. The results were still the same. The clams looked a bit stressed for the first few hours afterwards and then would look excellent with no pinching. Then, the pinching would start coming back after a couple days. I finally "gave up" on dipping my clams and decided I would let nature take its course. This was after my tank crashed over a year ago, but I never lost any clams. I had the clams in a quarantine tank and they started dying for no apparent reason. I would lose about 1 every week or 2. It wasn't until I was down to 3 that I finally found out it was my Foxface rabbitfish nipping at the mantles that was killing my clams. That was at the beginning of last summer.
At the end of the summer the clams were moved to a newly setup 400 gallon system. They now reside in a 40 gallon clam tank with no fish, which is connected to my main system. I have had all 3 of these clams for close to 2 years now. There is a 7" derasa, a 5" derasa, and a 4" maxima. When they went into the new system they all had the disease. However, after a few months the larger derasa and the crocea stopped pinching and have not pinched since. The smaller derasa still continues to pinch but grows pretty fast, which leads me to believe it is still "healthy" and the disease won't kill it.
I have absolutely no idea why two of the clams seemed to kick the disease but the other still has it. I wonder if they are eventually able to build up an immunity. One thing I'm sure of is that the disease is contagious. Back when I had 15 clams it started in 1 clam and slowly spread to the others. What is strange is that the 3 remaining clams are all within a few inches of each other but only the one continues to pinch. This is what makes me think the other two may have built up an immunity.
I'm glad we finally have a thread going with some people in the industry that are willing to get to the bottom of this once and for all. Thank you very much Barry. And thank you to everyone else who has contributed to this and other mantle pinching threads.