Capybaras are classified as fish in Catholic canon law, on the grounds that they spend their lives in water. I’m guessing that a party of conquistadors was on the verge of starvation and got their priest to petition the Vatican to issue a retroactive ruling in their favour.

I don’t have a source for this but I had been told it was in an attempt to try to convert Venezuelans to Catholicism

You don’t like the religion?

Here, we made the big dog a fish, are you happy now?