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https://www.theguardian.com/environment/2025/oct/27/murray-cod-tracked-swimming-australia-biggest-river-system>
"A young Murray cod has swum one of the longest ever recorded journeys for the
species, travelling about 900km through the Murray River, its streams and
backchannels.
Murray cod, Australia’s largest freshwater fish, grow up to 1.5 metres and can
live for half a century. Research by Victoria’s Arthur Rylah Institute has
shown the species, listed as vulnerable under federal environment laws, is
capable of covering extreme distances.
Dr Zeb Tonkin, a freshwater ecologist with the institute, said Murray cod had
huge cultural and conservation significance.
“They’re the apex predator of the Murray-Darling Basin,” he said.
In the years following a major mortality event due to low oxygen levels in
2016, researchers tagged about 70 juvenile cod using small audio tags – a bit
like a microchip on a cat or dog – enabling their movements to be tracked via
“listening stations” along the river and adjoining streams.
Initially, the young cod didn’t move far. “They basically hunkered down in
their nursery habitat,” Tonkin said. But as they approached maturity – about
the age of four, when they were 50cm long – several took off in search of a new
home range.
One champion swimmer, which the scientists dubbed “Arnie” in honour of
Australia’s multiple Olympic gold medallist Ariarne Titmus, left the entire
study area and kept swimming, he says. It later popped up over the border into
New South Wales.
Taking advantage of the removal of barriers during the 2022 floods, the cod
swam into the Wakool then the Niemur rivers before heading back towards home.
In all, the fish travelled nearly 900km in less than two years. It was most
recently tracked in late 2024 at a section of the mid-Murray, near Belsar
Island, just upstream of Euston, and appears to have settled there for the time
being.
“For this species, it’s the longest we’ve seen,” Tonkin said. “There’s a couple
of other species that we know do this as part of their life cycle regularly,
species like golden perch and silver perch.”
Murray cod tend to be thought of as a sedentary species and can often be found
hanging out near snags, or submerged logs. But as the research found, they also
move – in some cases hundreds of kilometres – to disperse and breed."
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
