In Spanish tapas cuisine, the preserved fish served in a vinegar marinade as boquerones en vinagre is anchovies.
Fresh anchovies are cleaned and filleted, then marinated in vinegar until their flesh turns pale and firms. They are typically finished with olive oil, garlic, and parsley and served chilled with bread or alongside other tapas. The preparation is especially common in bars in southern Spain and along the Mediterranean coast.
The Spanish word boquerón refers to a European anchovy, Engraulis encrasicolus. This is different from an anchovy that has been salted and matured until brown and intensely savory, although both products come from anchovy species.
Because the fish is not fully cooked by heat, food-safety practice matters: commercial or properly frozen fish is preferred to reduce parasite risk. The vinegar gives the tapa its bright, sharp flavor.