Federal Prisons:Mackerel Is The Currency of Choice
Prisoners need a proxy for the dollar because they're not allowed to possess cash. Money they get from prison jobs (which pay a maximum of 40 cents an hour) or family members goes into commissary accounts that let them buy things such as food and toiletries. After the smokes disappeared, inmates turned to other items on the commissary menu to use as currency.
Books of stamps were one easy alternative. Elsewhere in the West, prisoners use PowerBars or cans of tuna. But in much of the federal prison system, he says, mackerel has become the currency of choice.
HT: Clover Aguayo
Related: "The Economic Organization of a P.O.W. Camp" in Economica 1945, a classic article about the "cigarette currency" system that emerged in most POW camps in WWII
Related: The word "salary," and the expression "being worth one's salt," derive from the word "salt," which was once a commodity form of money.