Oysters
Oysters used to be a quick, inexpensive snack sold in street wagons in London, Paris, New York and other major cities. They were also served for free at bars as a quick snack.
Overfishing made oysters scarce, and the prices soon went up. Water pollution played a part as well, especially during the Industrial Revolution. Oysters are quite sensitive to the environment, and once we ruined their water, they became hard to find.
Keep in mind oysters take between two and three years to mature, so not even modern farms can catch up with the demand for the meaty shellfish.
