These Churches imposed fasts either for single days or for continuous periods.

When people fasted it meant that they were chiefly denied any form of meat, and therefore must eat fish if they were not content with oil, bread, or vegetables.

So that there was an enormous and increasing demand for fish, not only amongst those fortunate people who lived by the seashore, and could get it fresh whenever they liked, but among those who lived at a distance inland, and were still required to fast when the Church so directed.

Of course in many parts of Europe they could get freshwater fish from the rivers or lakes.

But the supply was not equal to the demand; and fish sent up from the seacoast soon went bad, so that the plan of salting and curing fish was adopted.