Animal Species:Common Jack Mackerel, Trachurus declivis (Jenyns, 1841)

The Common Jack Mackerel has an elongate body and a forked caudal fin. The Common Jack Mackerel is a pelagic species that occurs in Australia and New Zealand.

A school of Common Jack Mackerel at Kangaroo Island

Photographer: John Lewis © John Lewis

Standard Common Name

Common Jack Mackerel

Alternative Name/s

Cowanyoung, Greenback Horse Mackerel, Scaly Mackerel.


The Common Jack Mackerel has an elongate body and a forked caudal fin. The scales in both the curved and straight parts of the lateral line are enlarged and scute-like, but may be overgrown by smaller scales in larger individuals. An accessory lateral line runs close to the base of the dorsal fin as far posteriorly as the fifth to tenth dorsal fin ray. The first dorsal fin is shot-based with eight spines. The second dorsal fin is long-based with the terminal ray being enlarged and slightly separated from the rest of the fin.

The species is dark blue-green above and silver to grey below. There is a prominent black blotch on the rear of the operculum.

This species looks similar to the Yellowtail Scad. The Common Jack Mackerel is longer and more slender than the Yellowtail Scad and has a longer accessory lateral line (only reaches to below the first or second dorsal fin ray in the Yellowtail Scad).

Size range

It grows to at least 60 cm in length.


The Common Jack Mackerel is a pelagic species that occurs in Australia and New Zealand. In Australia it is known from southern Queensland, around the south of the country, and north to the central coast of Western Australia.

The map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums.  Source: Atlas of Living Australia.


Distribution by collection data

Ozcam map of Common Jack Mackerel specimens in the Australian Museums.

What does this mean?


The species is found in inshore waters as well as continental shelf and continental slope waters at depths from the surface to about 500 m.

Life cycle

The species can live for about 16 years.  It matures at 3-4 years.

Mating and reproduction

Spawning season is from December to March.



What does this mean?


  1. Gomon, M.F. in Gomon, M.F., Glover, C.J.M. & R.H. Kuiter (Eds). 1994. The Fishes of Australia's South Coast. State Print, Adelaide. Pp. 992.
  2. Hutchins, B. & R. Swainston. 1986. Sea Fishes of Southern Australia. Complete Field Guide for Anglers and Divers. Swainston Publishing. Pp. 180.
  3. Smith-Vaniz, W.F. Carangidae. in Carpenter, K.E. & V.H. Niem. 1999. The Living Marine Resources of the Western Central Pacific. Volume 4. Bony fishes part 2 (Mugilidae to Carangidae). FAO. Rome Pp. iii-v, 2069-2790.
  4. Wilson, D.T., Curtotti, R. & G.A. Begg.  2010.  Fishery Status Reports, 2009: status of fish stocks and fisheries managed by the Australian Government. Australian Bureau of Agricultural and Resource Economics - Bureau of Rural Sciences, Canberra.

Mark McGrouther , Collection Manager, Ichthyology
Last Updated:

Tags ichthyology, Common Jack Mackerel, Trachurus declivis, pelagic, Carangidae, fishes, Cowanyoung, Greenback Horse Mackerel, Scaly Mackerel, elongate, forked caudal fin, blue-green, silver underside, blotches/mottled, black blotch, 30 cm - 1 m, inshore water, continental shelf, continental slope,