This is most likely the origin:
In 1508, French poet Eloy d’Amerval referred to a poisson d’avril (April fool, literally “Fish of April”), possibly the first reference to the celebration in France. In the Middle Ages, New Year’s Day was celebrated on March 25 in most European towns. In some areas of France, New Year’s was a week-long holiday ending on April 1. Some writers suggest that April Fools’ originated because those who celebrated on January 1 made fun of those who celebrated on other dates. The use of January 1 as New Year’s Day was common in France by the mid-16th century, and this date was adopted officially in 1564 by the Edict of Roussillon.
https://en.wikipedia.org/wiki/April_Fools%27_Day
AdmSmith wrote:
This is most likely the origin:
Wow, very informative - t y 4 posting...