re: I need an emergency stock for seafood gumbo.

Lobster base or next time IF you have time instead of shrimp shells buy a package or two of frozen gumbo crabs and low simmer them for about an hour or two. Better than just shells and you can pick the crab meat and add to the gumbo or just put the crabs themselves in the gumbo after making the stock.

Just keep in mind that when using bases like that that they have a good bit of salt in them. Don't add salt before using bases.