Poisson d’Avril! That’s what we in FR say instead of "April Fool!" The time-honored joke is to somehow stick a paper fish to someone’s shoulder or back without them knowing it.
Just like our April Fools Day, the Poisson d’Avril jokeplaying is the result of the switch from the Julian calendar to that which we use nowadays, the Gregorian calendar. Under the Julian calendar, the new year started on April 1 and when the switch was made, there were those who refused to make the switch. The hepcats (continuing the old-timey theme) of the day then poked fun of those old stuck-in-the-mud Julian calendarites.
I’ve been to several websites trying to find out why the FR use a fish. Alas, none provides a definitive answer. Could be that the astrological sign Pisces is this time of year or because this is Lent and Christians were supposed to abstain from meat so the "gift" of a fish was on point. Got me. Got historians too.
I note that Germany, Belgium, Scotland and many other other predominantly European countries have similar April Fools Day customs.
Newmans of Leguevin 