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