I came upon the material that follows at A&E’s HISTORY website.

Seriously.

* * *

April Fools’ Day—occurring on April 1 each year—has been celebrated for several centuries by different cultures, though its exact origins remain a mystery. April Fools’ Day traditions include playing hoaxes or practical jokes on others, often yelling “April Fools!” at the end to clue in the subject of the April Fools’ Day prank. While its exact history is shrouded in mystery, the embrace of April Fools’ Day jokes by the media and major brands has ensured the unofficial holiday’s long life.

Some historians speculate that April Fools’ Day dates back to 1582, when France switched from the Julian calendar to the Gregorian calendar, as called for by the Council of Trent in 1563. In the Julian Calendar, as in the Hindu calendar, the new year began with the spring equinox around April 1.

People who were slow to get the news or failed to recognize that the start of the new year had moved to January 1 and continued to celebrate it during the last week of March through April 1 became the butt of jokes and hoaxes and were called “April fools.” These pranks included having paper fish placed on their backs and being referred to as “poisson d’avril” (April fish), said to symbolize a young, easily caught fish and a gullible person.

* * *

To learn more about April Fools’ Day, please click here.