OT Shellfish soupsauce

Hello; This does not have any direct bearuing on wines; however, the foreign gentleman (=me) has discovered that many contributors to the forum are neat hands in the kitchen and may be able to help me out on this one. I save up the shells from lobsters, crabs, cray fish and similar (simliar being langoustines) in the fridge to, eventually, have them out to make a shellfish soup - or a fonde. However, since the original shellfish were always (almost always) boiled in salt water, a fair amount of salt adheres to the shells. This is a problem, particularly if you want to make a reduction of the fond - salt accumuöates and the result is unpleasantly salty. Would it help any to dunk, or rinse, the shells in hot-boiling water? Since most of the flavours appear to be fat soluble, I would expect this to be feasable, without a deterioration of the taste of the final fond-reduction-soup. The problem would not appear if I were to cook all my shellfish from scratchy, i e, using living lobsters, crabs etc, but that is beyond my power. You don´t get much live shellfish in these parts of the world.