Poisson d’avril! April’s Fish? The expression is only used on April 1st, “April Fool’s Day” to say “I tricked you!”.
Long time ago, the New Year started on April 1. This tradition ended in 1564, when King Charles IX switched France to the Gregorian Calendar. Since that Edict, the year started on January 1st instead of April 1st.
Apparently, some people were not very happy with the Edict and decided to continue to celebrate the new year on April 1st. The ones who embraced the new calendar started to make fun of the reluctant ones and would gave them silly presents on that day.
The origin of the fish remains however quite unclear. Anyway, on April 1st, children usually make paper fishes and tape them on people’s backs. And that day, if you’re reading the newspaper, surfing on the internet, watching TV or listening to the radio, watch out for hoaxes!