I can tell you something vaguely related about fish that’s pretty interesting. In northern parts of the world like Scandinavia there’s not much UV radiation during winter months. Our bodies need UV to produce vitamin D and we can have serious health defects (like rickets) without it.

At some point it was recognized that eating fish, particularly those rich in Vitamin D, made people much healthier. So it was codified into their culture and traditions to eat these healthy fish. Often with preparations that would preserve the fish and its vitamin D content throughout the winter.