Andy,
There is a captive breeding program at the Bristol Zoo
Gardens, U.K., for the endangered Partula snails of French
Polynesia.
http://www.bristolzoo.org.uk/learning/animals/invertebrates/tree-snail
It is certainly easier to rear terrestrial snails than marine
mollusks, though I've seen captive bred Japanese Haliotis from
the Northwest U.S. raised in a variety of colors based on food
made available to the population.  They are quite beautiful
with no encrustations.  Freshwater Pomacea (Apple Snails) are
also raised by tropical fish breeders.  I guess if such a
thing would take hold, a grading designation would have to be
added for natural or captive bred specimens!
Rich


---- Original message ----
>Date: Tue, 13 Dec 2005 10:39:08 -0600
>From: Andy Rindsberg <[log in to unmask]>
>Subject: Re: Grading of shells
>To: [log in to unmask]
>
>How often do conchologists grow mollusks to adulthood
specifically to create
>gem shells? Moth and butterfly collectors do this frequently.
Some
>ecologists even promote the set-up of "butterfly farms" in
tropical regions.
>Ideally at least, these can help to sustain the populations
of rare animals
>and also the plants and habitats that they require, while
giving native
>people an income, motives to preserve the environment, and
pride in doing
>so. The farms send pupae to butterfly houses in other
countries for
>emergence on display, and some of them also kill insects
immediately after
>emergence to ensure perfect mounted specimens to sell to
collectors. At the
>end of the day, it's not very natural, and abuses could be
pointed out, but
>when applied properly, the farming does help to preserve
species and
>habitats that are increasingly under threat.
>
>Is anything analogous going on in conchology? For example,
are certain
>habitats protected specifically for the growth of specimens
for sale to
>collectors (as opposed to farms for pearl oysters or conchs)?
Are mollusks
>raised in aquaria or in pools to make gem-quality shells? Why
not?
>
>Concerning another aspect of shell grading, one would have to
apply the
>system carefully to fossils. Most species of fossils are not
available in
>gem or even fine condition, so a collector may rhapsodize
over a broken
>shell that is nevertheless the most complete and beautiful
example of its
>species. For instance, Pteria limula (Conrad, 1833) is common
in the middle
>Eocene Gosport Sand of Alabama, and as Conrad pointed out,
the shell is
>"very pearly and iridescent", but I don't think I've ever
seen a complete
>valve, much less a complete shell, of this fragile species.
Like antiquarian
>book dealers, we should admit to flaws ("this edition is
scarcely available
>in complete form") but also point out positive features ("the
usually
>missing frontispiece is present in this volume").
>
>Andrew K. Rindsberg
>Geological Survey of Alabama
>
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