fresh water clams

The FW clams that are available seldom thrive in an aquarium. They generally need cooler, cleaner waters than we can provide in a tropical setup, and require lots of small particles of food in the water--really tough to keep them fed without having water quality problems.

They are also not as cool as many expect--they don't do much, just bury themselves in the substrate (and prefer a mud or sand bottom, small gravel won't work for all species), sticking out their tongues to feed. You seldom see more than a bit of shell and a siphon.

Another consideration. Most all FW mussels are fish parasites as larvae. If yours do well, they may breed, and it's possible that the larvae will parasitize your fish. As with most parasites in a closed system, this will kill your fish.