My wife has a strange variation of the common seafood allergy; rather than being allergic to shellfish, she can only eat shellfish but reacts badly to finfish (trout, salmon, cod, etc.). I love seafood and would love to make some variations of common fish dishes I love, such as seafood soup. I'm fine with squid, clams, and such, but the poaching stock comes out way too thin. Is there a quality stock alternative from shellfish? I've tried canned clam juice from the grocery store, but the taste isn't as strong as I would like, and it's a lot of money for very little juice. I've considered picking up the dried shrimp from the Asian market and making a paste, although that won't have much clarity. Any suggestions? 
I don’t know if there are commercially available products, but you can always make your own. My mom would regularly make shrimp stock from the heads and shells of shrimp. You can use the shells of crabs, lobster, or other crustaceans.  I recommend steaming them, remove the meat, then put thr shells into a pot to simmer. You’ll want to just barely cover the shells with water, so you’re not diluting the stock with too much water.   If you want to further concentrate it, I would recommend straining it first, then reducing it. If you wanted to use dried shrimp, it would probably work just as well.  Just don’t make it into a paste, so you can strain them out easily. 