(Now you know...)
Let’s begin with the title. Just why do Catholics eat fish on Friday – or, better said, why do Catholics abstain from warm-blooded flesh meat on Friday? The obvious answer that every Catholic should know is that it is a penance imposed by the Church to commemorate the day of the Crucifixion of Our Lord – to enable us to make a small sacrifice for the incredible sacrifice He made for our salvation. Why, then, is fish allowed? The drawing of a symbolic fish in the dirt was a way that the early Christians knew each other when it was dangerous to admit in public that one was Christian. Our Lord cooked fish for His Apostles after His Resurrection, and most of these men were fishermen. After He established His Church, these fishermen became “fishers of men” for the Kingdom of God.