THE team at Narrandera Fisheries Centre decided something had to be done in the aftermath of fish kills in the Lower Darling near the Menindee Lakes.
The system was becoming increasingly stressed and the casualty count was mounting.
The centre's hatchery manager Matt McLellan was one of the first to put his hand up as an expert team of eight staff was assembled to rescue some of the surviving Murray cod.
"Where they were, they would have died," said Mr McLellan, who coordinated the rescue.
"We didn't know how we were going to manage it because we had never undertaken a rescue of that type in that area before, but that's the way it is when you're doing something for the first time.
"We knew they'd be stressed."
That was why, after the team had gathered specimens with the best hope of survival, candidates were placed in an oxygen-rich recovery tub for as long as five minutes before being transferred to a transport truck.
The truck in which they made the almost 600-kilometre journey was equipped with two 2500-litre tanks with electronic oxygen control.
When they first made it to Narrandera they were immediately put into individual salt treatment tanks with a salt content of eight grams per litre (to put that in a layman's perspective, seawater is 35g to the litre).
"It's a quarantine process," said Mr McLellan, "and it knocks the parasites off them".
They were then weighed, measured, sexed and micro-chipped and are now in breeding ponds that will be home for about the next five years.
The wild DNA of these precious survivors has been saved for the gene pool's posterity.
Future fingerlings
THE ponds in which the survivors are now living contain nesting boxes and there is a mixed population.
Initially, because of their territorial nature, they were separated.
Murray cod breed in late September and each female may lay 10,000 to 50,000 eggs.
It is generally about 10-14 days into the egg's development before they need to feed, because of the large yoke sac into which they make their way into open waters.
In captivity, the first feed they get to eat are artemia, or brine shrimp - a micro crustacean - that are hatched en-masse at Narrandera.
The newborns are fed on artemia for two to seven days then released into plankton-enriched ponds.
After six weeks in the ponds and at eight weeks of age, the 35 millimetre to 50mm fingerlings are ready for harvest.
The ponds are drained, the fish collected, counted, given a health check and sent to new homes, generally impoundments, dams somewhere in the state.
The Narrandera Fisheries Centre produces between 1.5 million and 2 million fingerlings a year.
Mr McLellan said the centre helped create fisheries across NSW and almost all of the fish in Blowering Dam, on the Tumut River, and Copeton Dam, on the Gwydir River, are direct descendants from the program.
These fisheries remain open all year, even while the rivers are declared off limits to allow unhindered spawning.
While the Menindee fish kills were no doubt catastrophic events, the Department of Primary Industries freshwater research leader Dr Katherine Cheshire insists its casualties "can be replaced in our lifetimes".
Ageing of dead fish from the disaster zone had most between the ages of eight and 25 years.
Huge investment
AGEING individuals is possible through harvesting "ear bones", or otoliths, and is now done on-site at Narrandera in a state-of-the-art laboratory opened in 2016.
To determine a fish's age the otolith is removed from the head and suspended in transparent, hardened resin to enable extremely thin slivers to be cut and studied under microscope.
The otolith grows in size with the fish and rings develop, a productive year is denoted by the thickness of a ring and the number of rings indicates the age of any particular fish.
The lab has advanced and expediated the work done at Narrandera and is now attracting the attention of international researchers.
Where once samples were sent to commercial labs and the wait for results could be weeks, now everything is done immediately and on-site.
The mutli-million-dollar investment was the latest addition to a facility that has been leading the way since the 1960s.
It is a facility of which current centre manager Martin Asmus is extremely proud.
Mr Asmus took over from the legendary John Lake, who had watched over the facility in the early 1960s, and for which the attached visitors' centre is named.
The Narrandera research station began life as a single tin shed in the 1950s.
Today the centre consists of a 60-hectare property and the new lab is capable of analysing environmental DNA.
From water samples, microfragments are analysed and from that what fish are present in that water can be determined.
"This is particularly useful for threatened or endangered species," said Mr Asmus.
"You can know they were there yesterday."
THE facilities available at Narrandera have attracted the attention of University of Technology Sydney student Laura Michie, who has just finished three weeks intensive research of cold water pollution in our rivers caused by relases from mass storages, or dams.
It's her second stint at the centre, having done a month last year also.
Ms Michie's work is important.
Mr Asmus said the linear effects of cold water pollution from upstream can affect waters as far downstream as Narrandera.
Dr Cheshire said cold water could affect the fish species that need a temperature cue to breed, Murray cod, for instance, need waters of between 19-20 degrees Celsius to spawn.
