A family tradition.
Here's a decent description.
https://www.foodnetwork.com/recipes/articles/feast-of-the-seven-fishes
In Southern Italy, (AND NAPOLI) celebrating Christmas Eve with a feast of seven fish dishes is a much-loved, age-old tradition. It's almost always a family affair, with generations of cooks in the kitchen and favorite foods that return year after year. But you don't have to be Italian to throw your own holiday seafood feast, and you don't have to stick with traditional recipes, either. Here, everything you need to know about the holiday, including its history and how to throw your very own party choose from our menu of recipes.
What Is Feast of the Seven Fishes?
The Feast of the Seven Fishes is an Italian-American Christmas Eve celebration that brings families together the same way Thanksgiving does with traditions that span generations, decades and oceans. Known in Italy as La Viglia, which translates to The Eve, as in December 24th, Christmas Eve, The Feast of the Seven Fishes isnt a religious celebration (unless your religion is worshipping at the altar of amazing food). It really is just a big fish-forward holiday meal that traces its roots back to Italy. There isnt a set menu but there are a few dishes most families include, and weve got lots of info here that will help you plan a Feast of the Seven Fishes that fits your lifestyle (and the size of your kitchen).
Epicurious is way over the top with 53 recipes.
I think you can imagine that the simplest dishes are the ones that first, second and third generation Italian-Americans will (or should!) know.
https://www.epicurious.com/holidays-events/italian-seafood-recipes-for-the-feast-of-the-seven-fishes-gallery
Buon Natale