Eating fish on Fridays is still a loosely observed custom of fasting (as in restricting yourself to a disciplined diet) among members of the Catholic and Anglican Churches. But what is the origin of this custom?
You might have heard the tale of a genius marketing plot by the early Catholics. Assuming that many of the abbeys and monasteries were situated near bodies of water, the Church made a fast of fish obligatory, to be held on Fridays. That was the day warm-blooded animals were spared. The reason for this fast on Fridays was - so the tale goes - to sell the fish that the monks fished out of the bodies of water near their premises to fill the coffers of the Church.
The true origin is a bit less business-focused.
Jesus was crucified on a Friday, and his death redeemed the sins of the world. Scripts from as early as the first century exist that mention the fasting on Friday to commemorate this sacrifice. Also, the depiction of fish was a secret symbol for the early Christians to recognise each other - a quick fish drawn into the sand with a stick would show those in the know who they are dealing with.
The practice of fasting was also a something of mind over matter for priests - if you can't control the urges of your belly, how can you control a church, a parish, a monastery?
Meanwhile, in England, back in 1522 after the Catholic Church refused to acknowledge Henry VIII's divorce from Catherine of Aragon, the King broke away from the religion and its traditions. All of a sudden, eating fish on Fridays became a political statement against the king, which was the reason why the "fish on Friday" custom took a nosedive.
The fishing industry was hurting so badly that his son - King Edward VI - reinstated fast days in the middle of the 16th century to encourage people to eat more fish, providing the ailing fishermen with a flourishing trade again.