And what brought about this change in attitude? The question of course refers to the Biblical prohibition against eating aquatic animals without fins and scales.
Thanks in advance.
The Book of Acts claims there was a council in Jerusalem in the 40s AD called by James, Peter, and Paul over whether Christians needed to follow Jewish law regarding issues like circumcision and dietary law. The answer was a clear no.
Acts 15:19 “It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God. 20 Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood. 21 For the law of Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath.”
Later Christians would view attempting to keep Jewish dietary laws as a sign of Judaizing, a sign your Christian movement believed that following the Laws of Moses was a viable supplement or alternative to Jesus' sacrifice as a path to salvation, and be harshly condemned
Tl;dr the Levitican dietary laws are part of God's covenant with the Jews. Christians are Gentiles and are under no obligation to follow that covenant.