Shorthead Lamprey, Mordacia mordax (Richardson 1846)

Other Names: Australian Lamprey, Murray Lamprey, Short-headed Lamprey

Shorthead Lamprey, Mordacia mordax. Source: Rudie Kuiter / Aquatic Photographics. License: All rights reserved


Primitive jawless fishes with naked eel-like bodies, two low dorsal fins far back on the body and 7 pairs of enlarged pore-like gill openings. They have eyes on top of their and prominent hood-like sructure overhanging the mouth.

The oral sucking disc is armed with tooth plates arranged in a radial pattern. Their ammocoete larvae are worm-like and lack eyes and teeth.

Shorthead Lampreys have an anadramous life cycle, spending parts of their life cycle in freshwater and in the sea. The adults spawn in freshwater, and their ammocoete larvae spend several years living in freshwater streams.

Following metamorphosis, they migrate downstream and spend most of their adult lives at sea, before returning to freshwater streams to breed.

Cite this page as:
Gomon, M.F. & Bray, D.J. 2023, Mordacia mordax in Fishes of Australia, accessed 17 Jun 2024,

Shorthead Lamprey, Mordacia mordax (Richardson 1846)

More Info


Occurs in freshwater and coastal marine environments of south-eastern Australia, from the river systems and offshore waters near Adelaide, South Australia, throughout Tasmania and Victoria, and north along the New South Wales to near Sydney. The range extends moderate distances upstream in coastal rivers. 

The life cycle is anadramous, where the post-larvae and premature adults are marine, and the other stages occur in freshwaters.


Body eel-like, lacking scales; gill openings are 7 enlarged pores; mouth modified into an oral disc with sharp horny teeth in 2 large plates each with 3 large teeth and a series of smaller plates radiating outwards around mouth with smaller teeth; rim of sucking disc without fleshy papillae; single median nostril on top of head; eyes dorsolaterally on head; ammocoetes (<12cm) lack eyes and have a single undivided dorsal fin.

The two dorsal fins are set well back near the tail; first with short base, 2nd longer, (2 or more times length of 1st); anus below and behind midpoint of 2nd dorsal fin, usually below posterior 3rd of fin; lacking pectoral, ventral and anal fins.


To 56 cm TL, although usually between 35-40 cm. Most adults are 300-440 mm when they migrate back to freshwater.

Ammocoete larvae begin metamorphosis between 100 and 140 mm.


The early post-larvae are greyish-brown above and silvery below. Young adults are bright blue above, with silvery sides and ventral surface. Mature adults are blue-grey above, silvery below and have orange teeth when in freshwater.


The ammocoete larvae filter feed on plankton, detritus and microalgae. The adults are parasitic on other fishes and attach to their host with the suctorial disc.

They use their toothy tongue to rasp flesh and feed on the body fluids and muscle of the host. The adults cease to feed during their migration back to freshwater rivers to spawn, surviving on stored fats and body tissues.


Adults return to freshwater rivers where they usually spawn in small, shallow creeks and streams with gravelly substrates. The female prepares a small depression or nest in the substrate and attaches herself to a rock with the oral disc. The male attaches to the female with his oral disc and wraps around her to squeeze out eggs before releasing sperm. Adults die shortly after spawning.

Newly hatched larvae (ammocoetes) drift downstream into slow-flowing areas and burrow into muddy substrates. The larvae grow to a maxixum length of 17 cm and metamorphose after 3 to 4 years. The young migrate downstream during late winter and spring, and spend most of their adult lives in estuaries or at sea.


In the past, small numbers of Shorthead lampreys caught in the Yarra River were sold commercially.


Not evaluated.

Similar Species

Although the two species of Mordacia are very similar, Nonparasitic Lampreys (Mordacia praecox) lack radial tooth plates, are smaller in size and spend their entire lives in freshwater streams of southeastern Australia.


The specific name is from the Latin mordax (=  biting, snappish), possibly in reference to the parasitic behavior and/or the whorl of serrated, cutting teeth of this species.

Species Citation

Petromyzon mordax Richardson 1846, Zool. Voy. Erebus and Terror 2: 62, pl. 38(3-6). Type locality: Tasmania.


Gomon, M.F. & Bray, D.J. 2023


Atlas of Living Australia

Shorthead Lamprey, Mordacia mordax (Richardson 1846)


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Quick Facts

CAAB Code:37003002


Conservation:IUCN Least Concern

Habitat:Freshwater, marine

Max Size:56cm TL


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CAAB distribution map