The stuffed and mounted Murray cod that adorn pub walls across Australia are the subject of a new investigation by a New South Wales ecologist.

Dr Paul Humphries from Charles Sturt University said taxidermic cod were like a time capsule of the Murray-Darling Basin's history.

Dr Humphries is searching for up to 300 of the wall-mounted fish as part a study into the river system's history.

"Most fish have a date and a location," Dr Humphries said.

"Often the person or people who caught it.

"So if we can get a chronology, a timeline, of dates and locations and then match that with the size of the fish, we can get a pretty good idea about what was around in the past.

"And I know some of the fish go back to the early part of the last century, 1800s some of them.

"It's a wonderful record of what existed in the past and dare I say what could exist in the future."

Dr Humphries said the cod also gave an insight into the evolving definition of what a "trophy fish" was.

"What it means is, that at a certain time, let's just say in the 1930s, what did people see in that local area as being a fish, that was big enough to be worth spending the time stuffing and putting it up on the pub wall to show their mates," he said.

"That changes over time as the size and numbers of fish changes over time."

Cod can be nominated through Dr Humphries' Facebook page, Stuffed Murray Cod In Pubs.