That's not strictly accurate. The lift-bros will eat it, as it is the cheapest source of protein. They are the ones that guarantee the marketability.

If it were truly the case that no one wanted it, it could not be used as money, as another good would quickly replace it.

Dudes trying to get swole inside usually trade junk food for more prison chow and milk with other inmates who cant get commissary, also weight stacks were removed in most state and fed yards like California, so they fill laundry bags with water in their cells as makeshift weights when guards aren't around.

Very interesting!

Mackerel would be worse than cigarettes as they are not divisible. It would also be a good source of Vitamin D if you were incarcerated in northern latitudes