When buying a new Tridacna clam, there are several details that are indicative of a healthy specimen. For one, look for tissue extension. A healthy clam will extend its mantle well beyond the limits of its shell. That said, also pay attention to potential over-extension, or gaping, of the clam, as this is a clear sign of distress. Be on the lookout for reactivity to shadows. If you pass your hand over a clam, thereby blocking out the light and casting a faint shadow, a normally healthy clam will react by withdrawing into its shell. Another sign of clam health is a distinct hole where the foot and byssal organ would normally be located. A clam may have sometimes be missing the foot, meaning it was either cast it off when the animal was stressed, or forcibly removed by whoever collected the clam. One last thing to pay attention to is the clam’s shell coloration at the growth edge. A healthy clam will have white colored shell material along the opening, indicating that it has a healthy growth rate. Clams without this white growth are not growing in a way that they should be, and are likely not healthy.