I've owned two derasa clams. Both lived for roughly seven years then started to fade and die. Both times I was crushed and have now sworn off this species. So, how long have you kept one?
Sorry to hear that. The longest I've had a derasa was 6 years still kind of small coming in at 10". I lost him in a mass clam wipe out. I now own 3 but have felt the same as you.