Why do Christians eat fish during Good Friday?

Catholics fast on Good Friday, and traditionally eat fish and not meat on Fridays during Lent. They used to be forbidden to eat meat every Friday, and depending upon their location and diocese, some still are. Good Friday is a fast day, where one goes without the usual luxuries as a form of penance, purification and remembrance of God's laws.
Christ died on Good Friday, so we observe that every Friday in Lent including Good Friday.