I want to know this too. I'm planning to try it when my tank matures in a few months. I have read that Tridachna actually do well with a supply of nitrogenous waste and have even been experimentally used as the SOLE source of biological filtration in an aquarium (mind you, it was a BIG clam!).
ok well i gues i will be the guinea pig, ill go and get either a maxima, corcea or dersea, tomorrow, and my cuttle is still making the net breeder his home, so if it turns out they have a sweet tooth for clams, then its no worry