Soup

If you have a pot with a built in steamer (like one for boiling pasta), you could use that to cook the fish then drain the solids.
Or cheesecloth, tied up.
Or a clean loosely woven cleaning cloth, which also can be tied.

I would use the same kind that you use to make cheese or milk. This way it adds the flavours but keeps the bits in. https://en.wikipedia.org/wiki/Cheesecloth

Otherwise I would recommand using fumé which is a kind of seafood broth.