A couple of things to start with (1) the link needs to be edited either by you Abj or anyone wanting to read the recipe by removing 'if' at the end of the link, and (2) tip 5 is missing in the recipe.
The clam juice is a flavour that I wouldn't be able to place as I have only had them once and they were canned. If you can't get fish stock, you could use a light chicken stock or just water. The salmon is being poached in the liquid and then taken out to the bowls. You are therefore making a fish stock however weak. Bring that process to the front of the recipe if you like. And you don't need to make fish stock from shrimp shells. Just get some fish heads or wings and boil them. For ease though, I would try chicken stock, or water and chicken stock. To my Western eye, it looks like a Westernised Asian soup anyway so the chicken stock should be okay. Hope that helps.
Too many restaurants, not enough time...