My favorite salmon fact is that salmon was really common in the West European rivers. They aren't there anymore due to damming, watermills and other industrialization slowing down the rivers causing them to contain more mud and sand rather than rocks.

https://historiek.net/komt-watermolen-deed-nederlandse-zalm-...

I've heard from multiple sources that even some old professions had rules about how often they can be force to eat salmon. For example this source talks about how messengers are protected and are only allowed to eat salmon 2-3 times a week. I've seen similar rules in an old dutch servants cook book.

http://www.gestolengrootmoeder.nl/wordpress/dienstboden-wild...