It's an air bladder but is usually just like the popular mackerel. The Pacific chub mackerel is caught in significant quantities off the Coastline of California, although the Atlantic chub mackerel is widely dispersed together both coasts of your North and South Atlantic. An 1835 illustration in the Atlantic mackerel. https://atlantic-mackerel-recipes55785.dailyblogzz.com/32288946/how-much-you-need-to-expect-you-ll-pay-for-a-good-live-mackerel-for-sale