Depending on the level of organics in the water it might 'spoil' and you'd have mass dieoff even on the relatively short plane ride back. I'd reccomend either using a small aerator or using newly mixed salt water before shipping. You will have die off regardless but if your aim is biodiversity you might lose most of it. Also fish and wildlife may not be too happy with you bringing foregin organisms back - you can risk carrying it on but who knows now what might happen. You might get it back to the states in atimely manner only to have customs seize your nice rock and lock it up for a few weeks.