In the Q&A department here at Catholic Answers, year in and year out we get what I like to think of as the seasonal questions. At Christmas someone will ask "What time is the midnight Mass?" (No kidding, and not as obvious an answer as you might think in many American parishes.) At Halloween, someone will want to know if the holiday is pagan. And, at Lent, not just "someone" but everyone seems to ask "Why do Catholics eat fish on the Fridays of Lent?"
The short answer has been provided by my colleague Jimmy Akin in his blog post The Law of Abstinence:
The word for "meat" in the original is carnis . . . which does not correspond exactly in meaning to the English word "meat." In contemporary English, "meat" tends to mean the flesh of any animal, whether it is a mammal, a bird, a fish, or what have you. But as used [in the text to which Jimmy refers], carnis refers only to the flesh of mammals and birds. It does not include the flesh of fish (or, for that matter, of reptiles, amphibians, or insects).
As helpful as is that answer for understanding current Church discipline on the issue, it is possible to wonder why fish has become so emblematic of Catholic dietary habits on Lenten Fridays, to such an extent that our modern secular world has taken note and annually markets discounted fast-food fish sandwiches during Lent.
Legends have cropped up, purporting to explain that "fish Fridays" were begun by Church officials who wanted to promote the fishing industry. Catholics who live in areas where fish is not as readily available for consumption have turned to the Vatican for dispensations to eat other aquatic animals, such as capybara and muskrat. The bottom line is that fish are a powerful symbol of Catholic identity. Why is that?
After his Resurrection and before his Ascension into heaven, Christ appeared a number of times to various groups of disciples (cf. 1 Cor. 15:3-9). One of the most detailed accounts of a post-Resurrection appearance is in John 21, when Jesus appeared on the beach after the disciples had spent a long, fruitless night fishing. Christ asked them if they had caught anything, and the disciples said no. So, he told them to lower their nets again. This time, they pulled up so many fish that they found it difficult to haul in the catch.
John immediately realizes that "It is the Lord!" (v. 7), and the disciples, led by Peter, scurry back to shore. On the beach, Jesus tells the men to "Come and have breakfast" (v. 12). After they have eaten, Jesus decides to test Peter's faith. Peter, if you will recall, had denied his Lord three times (cf. John 18:15-27); and so Jesus asked Peter three times, "Do you love me?" (John 21:15-19). Peter passes his test with flying colors, even if there could be points deducted for undue curiosity about another disciple's relationship with Jesus (vv. 21-23).
There is a small detail in the account that tends to pass by without a lot of notice. Jesus told the disciples to cast their nets, the disciples did so and hauled up a huge amount of fish. The disciples brought in their catch, but Jesus apparently did not use any of the disciples' fish for the breakfast he was preparing. When they got to shore, Jesus already had fish cooking on a charcoal fire, along with a side of bread (vv. 8-9).
Why did Jesus tell the disciples to toss down their nets again if he already had fish? There is likely a lot of deep spiritual meaning to that request that I can't get into here, the surface being that the catch acted as a sign to the disciples of his identity. For the purpose of this post, what interests me is that Christ already had fish to feed the disciples.
So far as I can tell, this seems to be the only place in the Gospels where Christ evidently provides food ex nihilo (Latin, "out of nothing"). The wine at Cana was transformed from water (John 2:7-9); the loaves and fish that prefigured the Eucharist were multiplied from those few donated by the crowd (John 6:5-11); the makings of the Last Supper, from which would come the Eucharist, were prepared by the disciples (Luke 22:7-8). Even the devil did not ask Jesus to provide himself food ex nihilo, only to change stones into bread (Matt. 4:2-4). Here though, after the Resurrection, Jesus does not feed the disciples with fish they have provided; he gives them fish that seems to have no earthly origin. It is one more sign of his divinity. In the centuries to come, the fish would become both a symbol of Christ and a code by which persecuted Christians knew they were among friends.
During Lent, we are reminded in a special way of our complete reliance on the Lord. We abstain and fast, we pray and give alms, we attend spiritual retreats, we seek out the sacraments. We store up graces the Church offers to sustain us on the journey. By eating fish on the Fridays of Lent, perhaps we also give fitting recognition to the fact that we have nothing to offer the Lord but ourselves, and he will in turn provide for us all that we need.