jack mackerel

:  any of several medium to large food and sport fishes (genus Trachurus): such asa :  a fish of the northern Pacific Ocean (Trachurus symmetricus) that is iridescent green or bluish above and silvery belowb :  a fish of the southern Pacific Ocean (Trachurus murphyi) that was formerly considered a subspecies (T. symmetricus murphyi) of the northern Pacific jack mackerelc :  a fish (Trachurus novaezelandiae) of Australian and New Zealand waters that has a yellow tail fin