On the 1st of April, everyone has to pay attention to avoid being the victim of practical jokes and general foolishness. It is the ideal day for children (and grown-ups alike!) to tell funny jokes to those around them, including family members, friends, teachers, neighbors, colleagues at work, etc.
Where this habit comes from is not certain. There are several theories, but why the symbolic of the fish remains pretty much a mystery.
In France, April Fools’ Day is known for the “poisson d’avril” (April Fish). That tradition dates back to 1564. The origin of the April Fish in France is quite obscure. Maybe it was reminiscent of the ichtus used by Christians in the Roman era.
Although not directly related to Easter, April Fools’ Day traditions are followed by all French children on 1 April. People use paper fish to play an April Fools trick. This involves sticking a paper fish onto the back of as many adults as possible. And then running away yelling “Poisson d’Avril !” (April Fish!). Yes you better check your back if you happen to be in France on that day!