Adult cod are active hunters, feeding on sand eels, whiting, haddock, small cod, squid, crabs, lobsters, mussels, worms, mackerel, and molluscs.
In the Baltic Sea the most important species[clarification needed] are Atlantic cod, herring, and sprat.[45] Many studies that analyze the stomach contents of these fish indicate that cod is the top predator, preying on the herring and sprat.[46][45] Sprat form particularly high concentrations in the Bornholm Basin in the southern Baltic Sea.[47] Although cod feed primarily on adult sprat, sprat tend to prey on the cod eggs and larvae.[48]