By Harold McGee
In general, seafood is more full-tasting than meats or freshwater fish, because ocean creatures accumulate amino acids to counterbalance the salinity of seawater. The flesh of ocean fish generally contains about the same amount of salty sodium as beef or trout, but three to ten times more free amino acids, notably sweet glycine and savory glutamate. Shellfish, sharks and rays, and members of the herring and mackerel family are especially rich in these amino acids. Because the salt content of seawater varies substantially— it’s high in the open ocean, lower near river mouths—the amino-acid content and therefore taste intensity of fish varies according to the waters they’re caught in.