Is it safe to put a clam you fould in your aquarium tank?

It is not. You should not put anything into your aquarium that you have found in the ocean. There are different bacteria and parasites in the ocean than found in your tank. In addition, the differences in PH balance and salinity are far greater. You not only risk the clam dying, but potentially killing off everything in your tank. There are quite a few beautiful species of clams available at your local Saltwater Fish store. Many are quite affordable and the expert at these stores can give you directions on how to acclimate your new tank item.