In Czech you typically have carp at dinner on Christmas Eve. Some people don’t like carp so they’ll serve some other type of fish..
I was told that tradition is you buy a live carp a few days before Christmas Eve and put him in your bath tub to swim around. The children sometimes name him, feed him, and treat him as a pet (well.. a wet smelly pet). And come Christmas Eve.. with much crying and tribulation (from the kids).. Daddy enters the bathroom and bashes the carp over the head and knocks the hell out of him. And then you cook it! Yum!
Nothing says Christmas like carp, wouldn’t you say? Luckily I escaped that tradition, and my mother-in-law made chicken for me and Peanut.