The World Federation One Stop Fiqh

Ruling 1840

If a person dives into the sea and brings out a creature and finds a gem in its stomach, in the event that the creature is like an oyster that by its nature can contain a gem, he must pay khums on it provided that its value reaches the niṣāb. If the creature has incidentally swallowed the gem, then the obligatory precaution is that one must pay khums on it even if its value does not reach the niṣāb.