
"The Basque History of the World is the illuminating story of an ancient and enigmatic people. Signs of their civilization existed well before the arrival of the Romans in 218 B.C., and though theories abound, no one has ever been able to determine their origins. Their ancient tongue, Euskera, is equally mysterious: It is the oldest living European language, and is related to no other language on Earth."--BOOK JACKET. "Yet despite their obscure origins and small numbers (2.4 million people today), the Basques have had a profound impact on Europe and the world for more than 2,000 years. Never seeking more land, they have nonetheless fiercely defended their own against invaders ranging from the Celts and Visigoths to Napoleon and Franco. They have always been a paradoxical blend of inbred tradition and worldly ambition, preserving their indigenous legal code, cuisine, literature - even their own hat and shoe - while at the same time striving immodestly to be leaders in the world."--BOOK JACKET.
Every person (back then) could observe farm animals had sex. Since no one had seen fish having sex, it was believed that fish spawned spontaneously from rivers/lakes/oceans and therefore were free from the animal version of "original sin". That's why so much effort was put into catching and preserving fish.
Source:
https://www.amazon.com/Cod-Biography-Fish-Changed-World-eboo...
Also history of food:
https://www.amazon.com/Salt-World-History-Mark-Kurlansky-ebo...
The author has a fascination with Basques & Basque history. Or maybe they really had a large influence in fishing and trans-Atlantic navigation. And that maybe they discovered the huge cod banks by Newfoundland before John Cabot did.
https://en.wikipedia.org/wiki/John_Cabot
Medieval people were not stupid. They observed that pickled vegetables preserved the veggies for months. And they observed that people who ate pickled vegetables got scurvy (vitamin C deficiency disease) at a much lower rate. The recipes didn't travel too far, so while sauerkraut and kimchi are both pickled cabbage, with different spices they are wildly different.