Here's your fun, fish, Friday fact! (try saying that 10 times in row!)
The French have a theory that traces the origin of the custom 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 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 April Fool's Day pranks. They also observe the custom of giving each other chocolate fish on April 1.