A trout hatchery in the Snowy Mountains has lost 30,000 fish due to high river temperatures and low rainfall, which a water ecologist has blamed on the effects of climate change.
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The NSW Department of Primary Industries, which oversees the Gaden Trout Hatchery outside of Jindabyne, confirmed the loss occurred when the Thredbo River hit temperatures of 28.5 degrees around January 26.
Trout are a northern hemisphere fish and begin to stress and die at 24 to 26 degrees, a department spokeswoman said.
"Fish deaths on this scale at Gaden have not been experienced in the last 20 years," she said
The department also blamed a lack of rainfall on the loss of the 30,000 fingerlings - baby fish - and 1000 broodstock fish, which are used for breeding.
University of Canberra Associate Professor Ben Kefford said it could be good news for native fish in the rivers who get eaten by the non-native trout.
"It will mean they have far less predation from the trout and competition for that matter," Dr Kefford said.
Dr Kefford said he had also witnessed dead trout in the Wellington River in the Victorian alps in January.
"It certainly doesn't surprise me," he said.
"It will be a consequence of a hot summer which is due to climate change and we've currently got very low flows in most of our rivers."
The low river flows were themselves attributable to a lack of rainfall.
He explained that less water meant it was easier for the heat in the air to warm that body of water up.
"If temperatures get hotter and we have increased periods of dry spells this is probably what's going to happen," he said.
Dr Kefford said trout were more susceptible to heat stress hence why they were placed out in mountain alpine streams.
While native fish had higher heat tolerances Dr Kefford said it wasn't well known what their limit was.
The department said the fingerlings lost in January represented three per cent of the entire department's annual stocking production.
"The fingerlings currently at the Gaden Hatchery are in good health and [the department's] fish stockings have continued across impoundments and streams across the state," the spokeswoman said.
"Gaden Hatchery staff did a fantastic job saving the remaining fingerlings by getting them into cooler water as soon as possible."
This summer was Australia's hottest on record with January beating previous heat records as Australians sweated through multiple heatwaves.
