Australian Lamprey

The Australian lamprey (Geotria australis), also widely called the pouched lamprey, is a jawless fish belonging to the ancient lamprey lineage (Petromyzontiformes), a group that diverged from other vertebrates hundreds of millions of years ago. It is anadromous, spending its adult parasitic phase feeding on other fish in coastal and open ocean waters of the Southern Hemisphere before migrating into freshwater rivers of southern Australia, Tasmania, New Zealand, and southern South America to spawn. Larvae, called ammocoetes, live buried in river sediment for several years before transforming into free-swimming adults. The species is notable for a fleshy throat pouch that develops in breeding males, a feature not seen in most other lamprey species.

• Elongated, eel-like, scaleless body; color shifts from silvery-blue at sea to bronze or olive in fresh water
• Circular, sucker-like mouth with concentric rings of small horny teeth, no jaws
• Seven round external gill openings behind the head, no gill cover
• Single or divided dorsal fin set far back on the body
• Breeding males develop a distinctive baggy throat pouch, unique among lampreys

The pouch on mature males is the clearest field mark separating this species from other Southern Hemisphere lampreys such as the short-headed lamprey, which lacks a throat pouch and has a shorter, blunter head.

Australian lampreys are anadromous, dividing their life between the open ocean and freshwater rivers. Adults spend one to two years at sea in temperate Southern Hemisphere waters off southern Australia, Tasmania, New Zealand, and southern South America, where they parasitize other fish. To spawn, they migrate into coastal rivers and streams, sometimes traveling long distances upstream over riffles and through pools. Ammocoete larvae then live for several years burrowed in silty or sandy river substrate, filter-feeding on detritus and algae before undergoing metamorphosis. The species requires unobstructed river access between the sea and suitable spawning gravel, making it sensitive to dams and other barriers, and its broad range spans cool temperate coastal waters across multiple continents.

As adults at sea, Australian lampreys are parasitic, attaching to other fish with their sucker mouth and rasping tongue to feed on blood and body fluids before releasing their host. During their upstream spawning migration they stop feeding entirely, relying on stored energy reserves. Spawning occurs in gravel nests built in flowing river sections, after which adults die, a life-history pattern known as semelparity. Ammocoete larvae are burrowing filter feeders, sieving detritus, algae, and microorganisms from river sediment for several years before undergoing a dramatic metamorphosis into the adult body form. As both parasites at sea and detritivores in rivers, the species links marine and freshwater food webs across its range.