The Port Jackson shark (Heterodontus portusjacksoni) is a nocturnal,[2] oviparous (egg laying) type of bullhead shark of the family Heterodontidae, found in the coastal region of southern Australia, including the waters off Port Jackson.

It has a large, blunt head with prominent forehead ridges and dark brown harness-like markings on a lighter grey-brown body,[3] and can grow up to 1.65 metres (5.5 ft) long.

[5] The Port Jackson shark is a migratory species, traveling south in the summer and returning north to breed in the winter.

Dubious reports exist of catchings as far north as Western Australia's York Sound.

[2] This species completes an annual migration to breed in coastal embayments with males arriving first in harbours and bays along Australia's coastline.

Port Jackson sharks can grow up to 1.65 metres (5.5 ft) long[4] and are similar to others of their genus, bearing a broad, blunt, flat head, an anal fin, and crests above its eyes.

However, the species possesses characteristics that make them easily identifiable, such as their teeth and the harness-like markings which run for a majority of their body length.

These teeth function to hold, break then crush and grind the shells of the mollusks and echinoderms upon which this species feeds.

Juveniles of the species have sharper teeth and their diet has a higher proportion of soft-bodied prey than adults.

Each of the second to the fifth gill arches supports a sheet of muscular and connective tissue called a septum.

Each lamella is equipped with tiny arteries that carry blood in a direction opposite to that of the water flowing over them.

To compensate for the relatively low concentration of dissolved oxygen in seawater, water passes over the secondary lamellae of sharks some 5% as fast as air that remains in contact with the equivalent gas exchange sites, such as the alveoli of the lungs found in humans.

This ability is unusual for sharks which mostly need to swim with their mouths open to force water over the gills.

The species has an annual breeding cycle which begins in late August and continues until the middle of November.

They have the ability to turn their stomachs inside out and spit it out of their mouths to get rid of any unwanted contents.

Juvenile Port Jackson sharks have more pointed teeth and feed on a higher proportion of soft-bodied prey than adults.

A captive study showed that these juveniles did not prefer to spend time next to other sharks, even when they were familiar with each other (i.e., tank mates).

[16] Some were bolder than others when exploring a novel environment and they also reacted differently to a stressful situation (in choosing a freeze or flight response).

[10] In October 2011 a man was bitten by a Port Jackson shark at Elwood Beach near Melbourne.