Common grilled fish include mackerel, hairtail, croaker and Pacific herring. Fish such as salmon, tuna, and herring are cooked and canned. Partial drying and salting is popular for the preservation of fish like herring and mackerel. Billions of salmon and herring eggs were also killed. Icelanders eat mostly haddock, plaice, halibut, herring, and shrimp. Other products include salmon, crab, and herring. Adult cod primarily feed on fish such as capelin and herring. In the Baltic Sea the most important prey species are herring and sprat. Fatty fish like herring and brisling are given the same treatment. Sprat are competitive with herring for the same food resources. Side dishes including pickled olives and herring may also be served. Eating herring eggs may cause cholera. Clupeiformes consist of 350 living species of herring and herring-like fishes. Popular salads include Russian Salad, vinaigrette and Dressed Herring. A single juvenile herring could never catch a large copepod.