Why are all of my clams dying???

[whatcaneyedo]

I just lost my other 5 year old crocea today. It actually belonged to a friend for 1-2 years before I got it so I guess it was probably more like 7 years old. It didn't show any signs of a problem until last night when I saw it spawning. I've had clams spawn before and not die so I wasn't too concerned. Its been about 3 months since I've had a clam die... I only have two left now. A little 3"maxima and a 5" derasa.