I have had freshwater clams for a year and a half. they are doing great, I have 35 in a 20 gal with a dozen ghost shrimp, 6 cardinal tetras, and an otocinclus. they stay between 1/2 and 3/4 buried in the gravel every now and then you will see one "walking" with its tongue. when one dies the ghost shrimp love it, they swarm the shell and even when the carcass floats a couple of shrimp will swim up to it and hang upside down on it. even the fish will take a few bites. I only feed the tank twice a day with a pinch of tropical flakes and an occasional algae wafer.