My Derasa's near-death experience

[AMWeets]

I got a Softball-sized Derasa from my friend Timmy77 about six weeks ago and he was doing great-nice, open mantle and none of his tankmates were bothering. I put him in the center of the front of the tank where I thought he would get the most direct light- I only have T5s in my 55 gallon at the moment. I came home from work one night and he had "walked" almost a foot away from where I had placed him. The next night, he was all the way in the corner, practically wedged between a rock and the front glass. I didn't want him there because he couldn't even open all the way. So (dipstick, yes....) I picked him up and moved him back where he was in the first place. Next night he was laying on his side. (not good) SO I set him back up. In the morning, he was back on his side. So I tipped him back up and his two halves slid apart. (BIG uh-oh...) I panicked, of course. I decided he needed a bra to hold him together, so I put him in a glass bowl with a piece of filter floss on one side to help support him. It has been about three weeks now and he looks really good, aside from the scar on his mantle where he "bit his tongue." Now I don't know if I should leave him in the bowl or put him back in the sand. Anyway, thought I would share my story.

[christensonjes]

Wow that is suprising it is still alive!

[capman]

I've had two derasa clams develop this hinge problem when they started to get large (about the size you describe), and I've heard of several other derasas that did the same thing. The first one lasted about a year after this problem developed, but it never really seemed to manage to open its shells properly, and so its mantle did not expand normally, and eventually it weakened and died. This was very sad. (the second one that developed this problem died in a tank disaster due to equipment failure and stupid system design - also sad, but for different reasons).

The thing is that bivalves don't use muscles to open their shells (muscles, in animals in general, cannot push - muscles can only pull). They depend on the springy nature of their hinges to open the shells. Their shells open when they relax their muscles (or when they die), and when they contract their muscles they close their shells (so, any bivalve whose shells are closed up is expending energy to keep closed up). When the hinge is broken down the only way for them to open their shells is to have gravity do it for them, and this depends on them sitting in just the perfect position with a bit of support around them to keep them from falling over (but support also tends to keep them from opening).

If yours is doing well sitting in a bowl, and is opening well and expanding its mantle normally, without tipping or slumping over to one side, then I think I'd leave it there.

My understanding is that once the hinge is broken they can't build a new one, but I don't really know for certain. I don't know why the hinges break down like this. I assumed that it had to do with mine getting crowded by corals and its growth slowed down or something, and that this led to problems, but I really don't know.

I always thought that maybe this problem could be fixed if pieces of some sort of springy material could be glued across from one shell to the other where the hinge is supposed to be, but I imagine the tension would have to be right. I never came up with a suitable material to use.

I did try gluing (with superglue) strips of nylon window screen across the hinge area to stabilize things. I think this might have helped, but this material was not springy, so it didn't really fix the problem.