There are dietary laws for Catholics, specifically about fasting and abstaining from meat consumption, but they vary wildly by region. For example, Canadian Catholics are permitted to eat meat on Friday if they perform an act of charity, read the Bible, or pray more than usual. Just make sure you're Canadian or else God will be mad.
There's a case to be made for them all being fish biologically speaking, too.
Of course, that case would also mean making chicken, beef, and all the other meat people typically eat would be fish, which might defeat the intent of the rule.
Originally Christians aren’t even supposed to eat pork like the Jews. But then the Romans be like 🤌 then God said “Okay okay chill, pork’s back on the menu except on Friday’s”