"Mackerel snapper" is a sectarian slur for Roman Catholics, originating in the United States in the 1850s. It referred to the Catholic discipline of Friday abstinence

Fasting and Abstinence in the Roman Catholic Church

For Roman Catholics, fasting is the reduction of one's intake of food to one full meal a day. This may or may not be accompanied by abstinence from meat when eating....

 from red meat and poultry, for which fish was substituted. That practice distinguished Catholics from other Christians, especially in North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, where Protestant churches prevailed and Catholics tended to be poor immigrants from Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, Poland

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

, and Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

.

Catholics are still called to abstain from meat on Ash Wednesday

Ash Wednesday

Ash Wednesday, in the calendar of Western Christianity, is the first day of Lent and occurs 46 days before Easter. It is a moveable fast, falling on a different date each year because it is dependent on the date of Easter...

, Good Friday

Good Friday

Good Friday , is a religious holiday observed primarily by Christians commemorating the crucifixion of Jesus Christ and his death at Calvary. The holiday is observed during Holy Week as part of the Paschal Triduum on the Friday preceding Easter Sunday, and may coincide with the Jewish observance of...

, and every Friday of Lent

Lent

In the Christian tradition, Lent is the period of the liturgical year from Ash Wednesday to Easter. The traditional purpose of Lent is the preparation of the believer – through prayer, repentance, almsgiving and self-denial – for the annual commemoration during Holy Week of the Death and...

. Fridays throughout the year are days of penance, but forms of penance may be substituted at the discretion of national bishops' conferences, and may include works of charity instead of abstaining from meat.

Examples

One example of the term's use comes from a letter to University of Notre Dame

University of Notre Dame

The University of Notre Dame du Lac is a Catholic research university located in Notre Dame, an unincorporated community north of the city of South Bend, in St. Joseph County, Indiana, United States...

's president Father Matthew Walsh, from an anonymous Klansman who was upset with the actions of Notre Dame students in breaking up a Klan rally in South Bend.

The term was also used by character in the motion picture Heaven Knows, Mr. Allison

Heaven Knows, Mr. Allison

Heaven Knows, Mr. Allison is a 1957 CinemaScope film which tells the story of two people stranded on an island in the Pacific Ocean during World War II....

, set in the South Pacific

Oceania

Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...

 during 1944 (the screenplay compares the rituals and commitment of the Roman Catholic Church and the United States Marine Corps). In the film, the unchurched U.S. Marine

United States Marine Corps

The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

 Corporal

Corporal

Corporal is a rank in use in some form by most militaries and by some police forces or other uniformed organizations. It is usually equivalent to NATO Rank Code OR-4....

 Allison (Robert Mitchum

Robert Mitchum

Robert Charles Durman Mitchum was an American film actor, author, composer and singer and is #23 on the American Film Institute's list of the greatest male American screen legends of all time...

) refers to some fellow Marines as "mackerel snappers" while talking with a Catholic nun, then catches himself and quickly explains away his faux pas

Faux pas

A faux pas is a violation of accepted social norms . Faux pas vary widely from culture to culture, and what is considered good manners in one culture can be considered a faux pas in another...

by stating that they were the "best Marines".