Record numbers of blood-sucking lamprey fish in Murray River system in Australia

Scientists have found an endangered native fish in record numbers in the Murray River system, which is great news for the environment and lamprey fish. Photo / Getty Images

An ancient, blood-sucking fish has made a comeback from near-extinction after record numbers were monitored in the Murray River system in southeastern Australia last year.

A study for the Department for Environment and Water recorded 91 pouched lamprey and four short-headed lamprey swimming from South Australia's Coorong through to the Murray River system between July and October.

It is the highest number of the ancient and native species ever monitored in Australia over winter.

Lamprey were feared to be almost extinct after the Millennium Drought (from 2001 to 2009), which caused more than three years of disconnection of the Lower Murray river system.

"After the drought … we were really struggling to find any lamprey in the system and we had some really big concerns about whether we had lost a couple of species from the Murray-Darling Basin," the department's programme leader for Coorong, Lower Lakes and Murray Mouth, Adrienne Rumbelow, told ABC.

However, a recently increased flow into the lower Murray system has allowed the living fossil to continue migrating.

Lamprey are anadromous, meaning they migrate up freshwater rivers from the sea to spawn.

Scientists such as Rumbelow have fitted the lamprey with tags for tracking.

The Murray-Darling Basin Authority describes the pouched lamprey's appearance as "medium-sized, slender and elongated, with a scaleless, eel-like body".

Adults range between 50cm and 70cm in length in freshwater situations and are larger than the short-headed lamprey.

"Lampreys lack jaws; instead adults have a well-developed suctorial oral disc with blunt teeth in irregular spirals.

"During the spawning run, adult males develop a large pouch below the head."

They feed on the blood and flesh of larger fish in the ocean.

"They have an oral disc with several quite savage-looking teeth inside and they use this to attach to larger fish out in the ocean, raft a hole then feed on blood and fluids and even chunks of flesh," said South Australian Research and Development Institute research scientist Chris Bice.

"They only feed in the marine environment and as soon as they move into freshwater [from saltwater] and start their upstream migration, they stop feeding.

"So, while they may look a bit savage, they are of no risk or danger to humans."