frigate mackerel (or bullet mackerel), a fish of the tuna family in the genus Auxis. There are believed to be two species, A. thazard and A. rochei, both cosmopolitan in warm waters but not identical (although nearly so) in physiognomy and distribution (e.g. it is only A. rochei which occurs in the Mediterranean). The common names for them are confusing, often reflecting doubt whether they count as mackerel or tuna.
A. thazard may be over 50 cm (20") long, A. rochei slightly less, but the usual size of either is around 35 cm (14"); so they are small in relation to most tuna. The pattern on their backs consists of dark bars or wavy lines.
