Christmas carp (German: Weihnachtskarpfen) is a traditional dish for Christmas Eve in Central Europe. In the regions where it is eaten, beliefs link its head to Christ’s torture instruments and protection against witches. The fish is traditionally kept in a bathtub before preparation to remove muddy flavours and is commonly fried or served in dishes like gefilte fish. In some regions, leftover bones are placed in fruit trees for spring growth and its scales are carried for good luck.

I woulda guess England. Dunno why.