Common Jack Mackerel 

Trachurus declivis (Jenyns, 1841)

View scientific description and taxonomy

Scientific Details

Dorsal fin spines/rays: VIII; I, 29-35
Anal fin spines/rays: II; I, 24-29
Caudal fin rays: 17
Pectoral fin rays: 20-21
Ventral fin spines/rays: I, 5
Lateral line: 71-89
Gill rakers: 11-16 + 32-34

Interpreting fin count meristics.
Spines are in Roman numerals and soft rays are in Arabic numerals. Spines and rays that are continuous in one fin are separated by a comma. Fin sections are separated by semicolons.

Detailed descriptions of fin count and other meristics are in:
Gomon. M.F., Bray, D.J. & Kuiter, R.H. (eds) (2008) Fishes of Australia's Southern Coast. Sydney : Reed New Holland 928 pp.

Order level detail.
A Large and highly diverse group of modern bony fishes many of which have a generalized perch like body form. Most have pelvic fins with one spine and 5 rays and the maxillary bone is excluded from the gape of the mouth. Interrelationships of the group are poorly understood and continue to be studied. They inhabit almost all aquatic habitats from high-altitude strams to the deep sea, although most are marine.

Family level detail.
Streamlined, active-swimming fishes, with fine smooth scales, a relatively short-based spinous first dorsal fin, a long-based soft-rayed second dorsal fin, a narrow tail base and a deeply forked tail; usually a detached pair of short spines before the anal fin. While adults usually inhabit coastal or near shore waters, juveniles are often far from land around floating debris or large planktonic invertebrates such as jellyfish. Many are highly valued gamefish and some are commercially important.



General Description

One of three species of the genus Trachurus found along the southern coast. The three are difficult to distinguish. All have strong scutes in the straight part of the lateral line, some scutes in the curved part, long falcate pectoral fins, an additional lateral line just below the dorsal fin base to the beginning of the second dorsal fin. The anterior raised part of the lateral line is parallel to the body margin, accessory lateral line below base of dorsal fin terminating below 5th-11th (usually 7th-9th) segmented rays. Dark blue green above, blending to silvery grey below the midline, with yellow tinges on scutes and fins; a black spot dorsally on hind margin of gill cover; back generally brownish in estuarine fish, more blue-green in coastal waters. To 50 cm.


These planktivores form large schools of uniformly-sized individuals. Smaller fishes usually occur at shallower depths.


From surface waters to depths of about 500 m.

Open water

Distribution guide

New Zealand and southern Australia.

Species Group

Fishes Trevallies and allies


Shallow (1-30 m)
Deep ( > 30 m)

Water Column

On or near sea floor Midwater

Max Size

50 cm

Commercial Species


Global Dispersal

Recorded in Australia

Conservation Status

  • DSE Advisory List : Not listed
  • EPBC Act 1999 : Not listed
  • IUCN Red List : Not listed


article author Bray, D.J.

Di Bray is a Senior Collection Manager of ichthyology at Museum Victoria.


article author Gomon, M.F.

Dr. Martin Gomon is a Senior Curator of ichthyology at Museum Victoria.


Cite this page as:
Bray, D.J. & Gomon, M.F., 2011, Common Jack Mackerel, Trachurus declivis, in Taxonomic Toolkit for marine life of Port Phillip Bay, Museum Victoria, accessed 18 Jul 2024,

Text: creative commons cc by licence