It’s generally seen as pretty hard to maintain filter-feeding bivalves long-term in an aquarium tank, in terms of diet (diverse phytoplankton), pH/alkalinity, and substrate (many are pretty specific in terms of conditions in which they burrow). You might have better luck with Corbicula sp. (“Asian clams”) which are quite generalist in their food, even being able to deposit feed by scraping the substrate. They are however quite invasive, so please don’t release them into the wild! Oysters on the other hand are usually found in mostly brackish or fully marine conditions, and would likely not be able to thrive long-term in fully fresh water. Usually they can only survive short bouts of freshening. Source: I study clams