Australian researchers doc a Murray cod swimming 860km in an unprecedented migration occasion

An Australian freshwater Murray cod has stunned scientists by swimming a marathon 860 kilometers (530 miles) alongside a serious river system—believed to be a report for the species.

The fish, named Arnie after Australia’s just lately retired Olympic champion Ariarne Titmus, was first tagged in early 2022 in Mullaroo Creek, about 13 hours’ drive west of Sydney, mentioned Arthur Rylah Institute researcher Zeb Tonkin.

Four years outdated and weighing in at 1.7 kilograms (3.7 kilos) on the time, it “took off” when floods hit the world within the spring of that 12 months, he mentioned, touring an preliminary 760 kilometers upstream in lower than two months.

The scaly river dweller, an apex water predator, was in a position to cowl longer distances as a result of boundaries had been eliminated alongside the Murray River to let flood waters move via.

“It basically provided free passage for fish,” mentioned Tonkin.

Arnie then circled in some unspecified time in the future previously 12 months, swimming one other 100 kilometers downstream in direction of dwelling.

Researchers solely found the extent of the fish’s travels when sharing information with colleagues a few weeks in the past.

“We’ve been working on these species for decades… and we haven’t come across that sort of scale of movement beforehand,” Tonkin mentioned.

“Probably the best we have seen a Murray cod do is around 160 kilometers.”

Understanding Murray cod permits researchers to adapt water flows to guard their surroundings, mentioned Tonkin, whose institute is a part of the state of Victoria’s division of vitality, surroundings and local weather motion.

The fish—not associated to ocean cod species—can stay greater than 48 years, develop to about 1.8 meters and weigh greater than 83 kilograms (183 kilos), in accordance with the federal government’s survey of Australian fish shares.

“If we see this species breeding, growing well, migrating well, it’s a pretty good indication that the ecosystem in general is pretty healthy,” Tonkin mentioned.

The decade-long fish tagging challenge works intently with the Mallee Catchment Management Authority. It is funded by the state-financed Living Murray program, managed by the Murray–Darling Basin Authority.

© 2025 AFP