Hi Gang,
 
To my amazement (and slight dismay), I found out last year at a Western
Australia pearl farm that the only reason for using fresh water pearl seeds
is so that they can X-ray the oysters and determine whether the seed has
"taken". Otherwise, they could  just as easily use oyster shell seeds,
except those do not show up in X-rays.
Much care and effort is lavished on the oysters (turning, cleaning) to
avoid diseases. And the pearl industry, like the diamond industry,
maintains a limited supply to keep prices up. With a different motivation,
farming of the oysters could (with some effort) eliminate the need to
harvest them.
 
 
John Wolff
2640 Breezewood Dr.
Lancaster, PA 17601, U.S.A.