I saw a program once about the capybara, the largest living species of rodent, common in parts of South America. They said that because the animal spends so much time in the water, the local people decided it was a fish so it was OK to eat it on Fridays.
Frog’s legs were fine under the Friday rule. They taste wonderful when paired with tomato and a lot of garlic, known as Frog’s Legs Provencal.