As everyone knows, in prison you use cigarettes as a medium of exchange. Except in 2004, federal prisons banned smoking. Ergo, they banned cigarettes. Ergo, you need a new medium of exchange. Thus, via Alex Tabarrok, the rise of the mackerel:
Mr. Muntz says he sold more than $1 million of mackerel for federal prison commissaries last year. It accounted for about half his commissary sales, he says, outstripping the canned tuna, crab, chicken and oysters he offers.
Unlike those more expensive delicacies, former prisoners say, the mack is a good stand-in for the greenback because each can (or pouch) costs about $1 and few — other than weight-lifters craving protein — want to eat it.
I can think of some good reasons for the rule preventing prisoners from holding cash (“Money they get from prison jobs . . . or family members goes into commissary accounts that let them buy things such as food and toiletries”) but the mackerel situation seems a bit absurd. It seems to me that the prison system ought to create an in-house currency like Disney Dollars or chips at a casino for prisoners to use as a medium of exchange.