They just write themselves, don’t they? 
But seriously, the ruling mentioned seems to have been a response to a question from the New World.
From Wikipedia:
“In the 17th century, based on a question raised by the Bishop of Quebec, the Roman Catholic Church ruled that the beaver was a fish for purposes of dietary law. Therefore, the general prohibition on the consumption of meat on Fridays did not apply to beaver meat. The legal basis for the decision probably rests with the Summa Theologica of Thomas Aquinas, which bases animal classification as much on habit as anatomy. This is similar to the Church’s classification of other semi-aquatic rodents, such as the capybara and muskrat.”
