Packs of Fish Catch On as Currency, Former Inmates Say; Officials Carp ...There's been a mackerel economy in federal prisons since about 2004, former inmates and some prison consultants say. That's when federal prisons prohibited smoking and, by default, the cigarette pack, which was the earlier gold standard. ...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. ...