if you do take the clam outta water for ANY time, no matter how short a period, make sure to burp it, shake it under water to get rid of any air bubbles. i put a clam from the qt into the dt today. was outta water less than 2 seconds, and released 4 bubbles when shaken.
when i was treating/scrubbing for snails, they might be in the air for a minute or 2, so burping was always necessary. didn't lose any.
remember, though, tridacnas gather in shallow water and are frequently exposed to rain, air, sun. crashing waves, etc. until the next tide covers them.
when bred in captivity, they are taken out of water for long periods of time [i read an hour at a time], while pulled apart and injected with a secret steroid to encourage sperm/egg release