Your clam probably died from slowly starving to death.theyre actually very complex creatures and really demanding.except for Tridacna,,(the only clam worth keeping). All clams,mussels,scallops etc, don't just filter water and they're good..clams filter very specific food items like nano larvae,and different sized food to as they get larger.8 months is nothing ,the oldest clam dated right now is 'ming" ..507 years old....