Medium sized, slender and elongated, with a scaleless, eel-like body. Adults are commonly 500–700 mm long in freshwater habitats (larger than the Short-headed lamprey). Two, low dorsal fins are situated well back on the body near the rounded caudal fin, and paired pectoral and pelvic fins are absent. Lampreys lack jaws; instead adults have a well-developed suctorial oral disc with blunt teeth in irregular spirals. Fimbriae (fringing filaments) are present surrounding the oral disc (absent in Short- headed lamprey), and the eyes of adults are lateral in position (rather than dorsolateral in Short-headed lamprey). Adults and ammocetes both have seven small oval gill apertures on each side of the body behind the head. Newly metamorphosed young adults are bright silvery with blue bands along the back. The bands persist throughout the marine phase and early in the return to freshwaters, before fading and disappearing, leaving the adults a muddy grey-brown. During the spawning run, adult males develop a large pouch below the head.
The larval juvenile life phase (ammocete) is usually less than 120 mm long, worm-like, lacks eyes and tooth plates, and the dorsal fins are very low, not extending very far above the body surface. Sandy-brown to blue in colour, these ammocetes are darker on the dorsal surface. They can be distinguished from ammocetes of the Short-headed lamprey by the position of the vent, which is below the start of the second dorsal fin.
Most of the adult life is spent at sea. Adults migrate upstream from the sea, usually in mid-winter, to breed. The spawning run can involve distances of hundreds of kilometres, and like the Short-headed lamprey is thought to be mainly by nocturnal movements. In the Basin it is most commonly recorded migrating upstream in winter at fishways on the Murray Barrages between the Coorong and Lower Lakes. Adults may move upstream rapidly and over large distances. PIT tagged individuals released at the Murray Barrages have been recorded as far upstream as Lock 11 at Mildura, having moved ~800 km upstream in ~ 3 months. Migration of tagged individuals through the Murray Barrages spanned July-early September with migration continuing upstream until at least mid-October. Individuals generally moved 4-20 km per day, but some moved >35 km per day. Riverine olfactory cues, including pheromones from juvenile lamprey are believed important in stimulating upstream migrations in northern hemisphere lamprey species. Whilst migration cues are unstudied for Pouched lamprey, the species is only encountered at the Murray Bar- rages during periods of freshwater discharge, suggesting freshwater-related migratory cues (e.g. decreasing salinity, increased flow) are likely also important for this species.
Little is known of many aspects of the species’ ecology in the Basin, so much of the information below is drawn from studies in Western Australia. The spawning run lasts for about 15–16 months, before spawning the following spring. As adults cease to feed once entering freshwaters, the mean lengths of individuals declined by ~29% in females and ~14% in males with weights declining ~45% in females and ~10% for males over the spawning migration. This shrinkage is a result of the animal cannibalising its lipid, protein and glycogen reserves to derive energy and for the development of ovaries/eggs and secondary sexual characteristics (e.g. gular pouch and large suctorial disc in males). Details of spawning locations are not known in Australia but probably include the main channel of the River Murray and tributary streams such as Currency Creek and the Finniss River in the Mount Lofty Ranges. Adults die after spawning (but not immediately: see below). Females lay on average 58,000 eggs, which are small (~1.1 mm diameter). Recent New Zealand research has located wild spawning sites for the first time. Eggs were deposited in late Oct/early Nov in a coagulated cluster that was completely concealed and adhered to the underside of large boulders. Eggs were cream-coloured, slightly oval in shape, and commenced hatching after about 6 weeks. The male parent was observed caring for/guarding the eggs and both the male and female lamprey stayed at the spawning site until the larvae had dispersed. Adults survived for >105 days after spawning in the wild and >511 days in aquaria. Wild spawning behaviour is unknown in Australia, but in aquaria males demonstrated aggressive behaviour towards each other, with the same male and female mating on several occasions. Mating behaviour involved the male coiling around the female with his vent close to the female’s cloaca, with twisting and vibration leading to egg release and simultaneous sperm release.
The juveniles (ammocetes) are toothless, probably feeding on algae, detritus and micro-organisms filtered from the water. Ammocetes are sedentary, and live in soft substrates (mud and silt) for about 4.25 years, before metamorphosing (at around 80– 120 mm length) and migrating down to the sea, usually in late winter. As adults in marine habitats, pouched lamprey is parasitic on other fish, rasping a hole in the side and feeding on blood and/or muscle.
The Pouched lamprey has the widest distribution of all lampreys, with a wide southern temperate distribution including Australia, New Zealand and Chile. Previous records from Argentina are now considered a separate species. Globally its conservation status is unclear. However, it is known to have declined in Australia and New Zealand. It is listed as Endangered in the Action Plan for South Australian Fishes and is considered ‘vulnerable’ under the Adelaide and Mount Lofty Ranges national recovery plan. In recent decades this species was rarely recorded in the Basin because of its cryptic habits, limited connectivity between freshwater and marine habitats and potential absence of migratory cues. Historically, it could be seen in large numbers on spawning runs in the lower Murray at migration barriers such as weirs. The installation of fishways on the Murray Bar- rages and the completion of the Sea to Hume fish passage program means the species is likely to be recorded in more upstream locations in coming years. The 2020/21 catch of this species in the Coorong-Lower Lakes monitoring program was the highest since the program’s first year in 2006/07. Also found in coastal rivers in Vic, SA, Tas and WA. The species was not recorded in the Sustainable River Audit (2004– 2013) or MDB Fish Survey (2014/15–2021/22).
Barriers to fish movement can interfere with spawning migrations, although the species can climb wet vertical surfaces. Lack of fresh- water outflows from the barrages and Murray Mouth during the winter upstream migration season probably limits cues for movement from marine to freshwater habitats. It is listed as Endangered in the Action Plan for South Australian Fishes, considered Rare by the SA Department for Environment and Water. It is listed globally as Data Deficient by the IUCN Red List with populations having declined in Australia and New Zealand but population trajectory in South America is unknown.
Allen et al. 2002; Baker et al. 2017; Bice et al. 2016a, 2019, 2020 a,b 2021; Cadwallader & Backhouse 1983; Hammer 2004; Hammer et al. 2009; Hardisty et al. 1986; Koehn & O’Connor 1990; Miller et al. 2021; Paton et al. 2019, 2020; Potter 1996b; Potter et al. 1996; Riva-Rossi et al. 2020; Wedderburn & Hammer 2003; Wedderburn et al. 2017; Zampatti et al. 2010; C. Bice & B. Zampatti unpubl. data.
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