Here in the Driftless Area, it’s still Dec. 24, so a Christmas Eve post is in order. Prior to the calendar reforms of Pope Pius XII (I think; maybe St. John XXIII?), the Christmas Vigil was a day of abstinence from meat, just like Fridays and Lenten weekdays. In America at least, it became traditional to eat oyster stew on Christmas Eve. Just like Friday fish fries, Christmas Eve oyster stew seems to have spread beyond Catholic circles to the culture at large. I remember eating oyster stew on Christmas Eve when I was a child. My mother and I had oyster stew tonight.
Here’s a New Liturgical Movement article about the Christmas Vigil as a liturgical observance: http://www.newliturgicalmovement.org/2016/12/liturgical-notes-on-vigil-of-christmas.html The author, Gregory DiPippo, points out the penitential nature of the vigil (no Gloria or Alleluia at Mass, etc.).
Here’s an article about the American tradition of oyster stew on Christmas Eve: http://www.history.com/news/hungry-history/oyster-stew-on-christmas-eve-an-american-tradition This article traces the tradition to Catholic Irish immigrants who substituted oysters for the “ling” fish they traditionally ate in Christmas Eve stew back in Ireland.