Adam Kerezsy, The Riverine Grazier
As anyone with an interest knows, the inland rivers of Australia’s Murray-Darling Basin are already well-inhabited by invasive – or alien – species.
The most obvious are the massive carp that shuffle and slurp along riverbanks in spring and summer, but there are also others: goldfish as big as footballs, predatory redfin and trout, and small (4 centimetre) gambusia or mosquito fish all contribute to the mix and effectively make life difficult for our native species.
Unfortunately, in the Lachlan, there’s a new kid on the block.
Oriental weatherloach (pictured above) is an eel-like animal from Asia that started off in Australia as an aquarium fish.
As early as the 1980s, wild breeding populations were detected in Victoria, and by the time the floods ended the Millennium Drought, they’d spread throughout the Murray to South Australia, and were established along the Murrumbidgee.
Weatherloach were first found in the Great Cumbung Swamp – where the Lachlan meets the Murrumbidgee – in the first decades of this century, but during a recent survey they were detected upstream of the Oxley Weir.
This means that upstream colonisation of the Lachlan is a likely outcome in subsequent years.
Weatherloach live on the bottom of rivers and lakes, so pose a direct threat to animals that either live or nest close to the substrate. This means that catfish, Murray cod and a couple of smaller native species are all in the firing line.
Unfortunately, weatherloach also have a super-power that other fish mostly lack: they don’t need much oxygen in the water, and can actually survive out of the water for short periods.
This means that weatherloach can reach small and isolated ponds where frogs and other floodplain animals may be breeding.
So if fishers see an eel-like creature in their shrimp pots or landholders notice them squirming between puddles after the rain, the chances are that the loaches have indeed ‘landed’ in the Lachlan.
And if they haven’t – yet – it may only be a matter of time.
This article appeared in The Riverine Grazier, 22 October 2025.
