"April Fools" in France: When my husband was young, he and his classmates would play tricks on each other by taping paper or aluminum fish (poisson) on the back of each others coats or would hang a paper fish around a friend's neck. If you fell victim, the others would erupt in playful laughter. He also has fond memories of chocolate fish being sold at the local chocolatier. Not a bad tradition if you ask me!
The linkage between April Fools Day and fish goes back to the abundance of fish to be found in French streams and rivers during early April when the young fish had just hatched. These young fish were easy to fool with a hook and lure. Therefore, the French called them 'Poisson d'Avril' or 'April Fish.' Soon it became customary (according to this origin theory) to fool people on April 1, as a way of celebrating the abundance of foolish fish. The French still use the term 'Poisson d'Avril' to describe the unfortunate victims of April Fool's Day pranks.
It felt only appropriate to have a tuna sandwich for lunch today since the diet forbids me from indulging on a chocolate fish! I'm holding out for that box of Chocolates that will be sent from the in-laws in France to us for Pâques (Easter).