A stubborn little fish in the Murray River has stunned local researchers after being coughed up in one piece by a large cod.

Department of Sustainability and Environment researchers Matthew Jones and John McKenzie were electro-fishing around snags at Lock 11 on the Murray River near Mildura last week when they pulled out a 1.2 metre long Murray Cod.

But if its sheer size wasn't enough to marvel at, the massive cod cough up its latest meal still intact.

“It was a big cod but it’s not unusual for us to find fish that big, but when we got this one on board it coughed up a 40cm long Golden Perch (Macquaria ambigua) that was still alive,” Dr Jones said.

“Occasionally we see a large Murray cod coughing up a small dead fish, but this perch was more than a foot long and alive.

“It was definitely a first for both of us and we just looked at each other in disbelief. It must have been breakfast for the big Murray Cod.”

The researchers said the perch was a picture of healthy, swimming alongside other fish in their live-well in their boat.

The perch was eventually tagged and released with the other fish.

“Despite the ordeal of being eaten by a cod, shocked by the electrofisher and tagged, the lucky perch still swam away," Dr Jones said.

Dr Matthew Jones heads up the Victorian component of the Murray River Fishways Assessment Program (MRFAP).

The program looks into the impacts of native fish to the Murray-Darling Basin’s fishway installation program, which is aiming to restore fish passage in the Murray.

They hope to open up 2225 km of river for fish to migrate between the Goolwa barrages in South Australia and the Hume dam, near Albury.

Local anglers are urged to tag captured fish then record the date, capture location, species and tag number and ring through the details on the free number (1800 134 093).

Anglers who do so will receive a reward and information on the movement behaviour of the recaptured fish.