November 18, 1966. The Latin Rite of the Catholic Church relaxes the Abstention Rule.

Smelt being eaten by members of Congress and their guests.

On this day the Latin Rite Catholic Bishops of the United States relaxed the rule on abstaining from meat on Fridays throughout the year.  This followed a Papal direction in 1962 that the Friday penitential requirement be adopted to local conditions, reflecting  a move by the Church focused on that goal. The same move resulted in the vernacular replacing Latin in the Mass at about the same time.

In the case of the Catholic Bishops of the United States the removal has created some confusion.  Fridays retain their penitential character and Catholics are urged to substitute something for abstaining from meat but few do.  Indeed, there's debate on whether there's any requirement to do and the fine, orthodox, Catholic apologist maintains there is not.  Some others maintain there very much is, with those holding that view tending towards the Catholic Trad community.

To the surprise of American "Roman" Catholics, the rule was not done away with globally and it remains a matter of Church law in many other localities in the world.  It also remains one, of course, during Lent.

There are a lot of rumors in the Protestant world about this practice, a lot of which are frankly absurd.  Old anti Catholic myths regarding fish on Fridays were one of the things that I still heard in school when I was a teen, usually centered around some completely bogus economic theory.  The actual basic reason for the practice is that it was a remaining Latin Rite penitential practice of which there had once been many, but which had dwindled down to just a few in the Latin Rite over time.  In the Eastern Rite and the Orthodox Churches, however, they remain numerous and occur throughout the year.

Indeed, the practice in the Eastern Rite and Orthodox Churches is instructive in that their fasts often extend beyond abstaining from meat and to other things.  During Great Lent, for example, they ultimately extend to oils, dairy and alcohol.  

The reason for abstention from meat (there was never any requirement that people actually eat fish) reflected the logistical economy of an earlier time.  Today fish is readily available on the table no matter where you are, but in earlier times this wasn't so.  Abstention from meat limited diets and protein sources other than fish were regarded, and frankly usually still are, as more celebratory.  People like fish, of course, but not too many people are going to sit down to a big Thanksgiving dinner of flounder.  The goal wasn't to starve people, but to focus on penance while still sustaining their needs.  Limiting food to the plain, and fish for most people, if available, was plain, emphasized that.

As with a lot of things, over time in Protestant countries this practice tended to mark Catholics and also became subject to silly myths.  Even now, over fifty years after the practice was relaxed in the United States, you'll occasionally find somebody who will insult Catholics with a derogatory nickname from the era related to fish.  Likewise, like a lot of dietary practices that have long ceased, people born far too late to really experience "fish on Fridays" will claim they did.

Ironically, of course, fish has gone from a less favored food even fifty years ago to a dietary and culturally prized one.  It's one of the odd ways in which the religious practices of Catholics, to include fasting, has come back around as a secular health practice.  And as Catholic orthodoxy has returned as the Baby Boomers wane, fish on Fridays has been reintroduced voluntarily among some orthodox or simply observant Catholics, even where they are not required to do it.