Short-headed Lamprey

The short-headed lamprey (Mordacia mordax) is a jawless fish native to southeastern Australia and Tasmania, one of only three lamprey species found in the region. It is a member of the family Mordaciidae, distinct from the more widespread pouched lamprey, and is named for its comparatively short, blunt head relative to body length. Like other Southern Hemisphere lampreys, it is anadromous, spending an adult parasitic phase feeding on fish in coastal and estuarine waters before migrating into freshwater rivers to spawn. Larvae, called ammocoetes, live buried in river sediment for several years before transforming into free-swimming adults. The species belongs to the ancient jawless fish order Petromyzontiformes, lacking true jaws, paired fins, and a bony vertebral skeleton.

• Slender, scaleless, eel-like body, olive-grey to brownish in color
• Notably short, blunt head relative to body length, the source of its common name
• Circular sucking-disc mouth with rows of small teeth, differently arranged than in pouched lamprey
• Seven round gill openings behind the head
• No throat pouch in males, unlike the related pouched lamprey (Geotria australis)

The short-headed lamprey is most easily separated from the similarly ranged pouched lamprey by its shorter head, more compact snout, and the complete absence of a male throat pouch during the breeding season.

Short-headed lampreys are anadromous, occupying coastal and estuarine marine waters of southeastern Australia and Tasmania during their adult parasitic feeding phase before migrating into freshwater rivers to spawn. Their range includes rivers draining into the Tasman Sea and Bass Strait, where they require unobstructed passage between the ocean and suitable upstream spawning gravel. Ammocoete larvae burrow into silty or sandy sediment in slower sections of these rivers, where they filter-feed for several years before metamorphosing. The species depends on both healthy coastal marine habitat and clean, connected river systems, making it vulnerable to dams, weirs, and river degradation across parts of its range.

As adults at sea, short-headed lampreys behave parasitically, attaching to fish with their sucker mouth and using rasping teeth to feed on host tissue and body fluids. Once they begin their upstream spawning migration, they stop feeding entirely, living off stored energy reserves for the remainder of their life. On reaching suitable freshwater gravel habitat, pairs construct simple nest depressions by shifting stones, spawn, and die shortly afterward, a single-reproduction life history typical of lampreys. The burrowing ammocoete larvae that result are filter feeders, straining algae, detritus, and microorganisms from river sediment for several years before undergoing metamorphosis into the adult form, linking marine and freshwater food webs in southeastern Australia.