The processing depends on the type of product, and in Denmark it is relevant to distinguish between the processing of demersal fish (mainly codfish and flatfish), the processing of pelagic fish (e.g. herring and mackerel), and the processing of shellfish (e.g. shrimp, prawn, lobster and mussels). The processing of demersal fish is typically relatively simple while pelagic fish are often processed into more refined products, such as pickled herring and canned mackerel, which involve more processing.