Wayne Harland wrote,
"I've noticed that many of the algae feeding mollusks (Astraea, Tegula,
Turbo etc) have a remarkable tendency to be quite aromatic when cleaned.
 However, when boiled quickly after capture as opposed to the "rotting"
method, the smells are not nearly as offensive.  Additionally, even the
Strombus (another algae eater) when allowed to rot are no walk in the park
either."
 
He has a good point. Pond scum (algae floating on freshwater lakes) often
smells strongly fishy, and I have sometimes wondered whether fish acquire
this smell by transferring chemicals up the food chain. The malodorous
chemical or chemicals are very long-lived. Dried specimens of mollusks
retain their smell for decades. Even the interiors of painted metal
cabinets used to hold them two decades ago still smell of rotting mollusk,
despite efforts to clean them and air them out.
 
Also, people who eat fish at every meal can also acquire a fishy odor. I
experienced this on a field trip to (LOCATION DELETED), but as everyone
smelled the same and were all geologists, nobody cared. In fact (I hesitate
to admit this, but it's true), the fishy odor actually smelled delicious,
reminding me of the wonderful meals we were eating. Anyway, you are what
you eat, whether you're a fish or a human being.
 
As to stinking "shells", I have never encountered anything quite so bad as
the carcasses of terrestrial turtles, even among politicians or university
presidents. I don't know what they eat, but I can't recommend it.
 
Andrew K. Rindsberg
Geological Survey of Alabama