Movida's Shellfish Fumet recipe is based on a classic fish stock - cod and hake bones are roasted before being simmered for hours with tomatoes, white wine and giant squid. The stock is then finish with fresh red prawn heads, leeks, garlic and paprika. The result is an incredibly rich, full flavoured fumet.
Of course you have paella in mind, but it's amazing in most things that call for fish stock. Although it's intensity pushes it more towards the rustic and hearty side of seafood than the light and delicate - think of the style of seafood soups of the Catalan coast like Zarzuela or Romesco de Peix.