"Mackerel snapper" was once a sectarian slur for Roman Catholics, originating in the United States in the 1850s. It referred to the Catholic discipline of Friday abstinence from red meat and poultry, for which fish was substituted. That practice distinguished Catholics from other Christians, especially in North America, where Protestant churches prevailed and Catholics tended to be poor immigrants from Italy, Poland, and Ireland. The term has been considered jocular since the mid-20th century and has fallen into disuse.