General News
3 December, 2025
River blackfish a struggling species
THE river blackfish used to be abundant in south west Victoria and has now become scarce, a topic which a Deakin University student recently touched on in his honour’s thesis, including ways the community can help to save the current population.
Tim Vincent wrote his thesis about understanding the medium-to-long-term impacts of willow removal in the Gellibrand River catchment.
“Starting about 25-26 years ago, the Catchment Management Authority basically removed a whole lot of willow trees, which are introduced species, from the sides of the rivers and then began planting native trees,” he said.
“We’re wanting to see what the long-term effects of that are on the fish species.
“The blackfish are pretty closely linked to habitat and the Gellibrand has always been a stronghold population so it’s been regarded nationally as the river for blackfish.
“Back in the 80s it was really well studied – they were really abundant in there and people came from all across Victoria to catch them.
“People started to notice declines a long time ago – 90s, 2000s – and one of the things they thought was maybe the willow trees had something to do with it, or maybe ripping out the willow trees had something to do with it.”
One of the things Mr Vincent noticed from the study was different fish species thrived in different parts of the river depending on the shading conditions.
“In the willow cleared sites, in the farmland, the streams there, they get a lot of sunlight, a lot of plant growth, but there’s no trees to shade it, so we’re finding things like pygmy perch and eels,” he said.
“Then in the forested sites where there’s tree cover the water is a bit cooler and faster, we’re finding a lot more of the blackfish.
“As the trees grow and mature, the fish communities are changing as well.”
Mr Vincent said fencing off waterways and removing willow trees incrementally were things people could do to help the species.
“Fence off the waterways from cattle – if you’ve got land and a river running through it, that makes a huge difference,” he said.
“Removing willow trees is certainly a good idea and I’m probably no expert in the field – but not ripping out the whole section of willows at once and then replanting, because you’re taking away these mature trees that have got shade over the river and then replanting with something that’s young and small.
“You could see it down there on the creek, a lot of those rivers that cattle could just walk straight into, the banks are trampled, they’re muddy, they look nothing like the natural sites do.
“Blackfish need a lot of tree cover, snags and logs in the water, things they can hide under from predators, bits of shade and undercut banks, and you just don’t get that in the farmland.”
Steve Mueller has dedicated his life to studying the river blackfish and has turned his property into a breeding ground for the fish – in fact, he’s the first person to successfully breed blackfish in captivity.
“We’ve virtually got a fish that lived in ancient times now trying to live in modern times and it’s just not working out for them,” he said.
“The only way I can see to recover this stock, because they breed so slow, is we need to work out how to breed them to then get them back into the waterways, and what I’m trying to do is find a way to breed them in basic farm troughs.
“There’s a lot of complications involved even in that, because if you have a mature blackfish pair that breed, then you either take out the mature fish and put them somewhere else because they’ll eat their young, or you take out the young.
“You can’t catch and put the young straight back out into the water because we’ve got trout and redfin in most of these creeks and streams now, and they wouldn’t last a week.
“So we’re probably at the stage where we’re going to have to have another tank where we can grow them out to a bigger size and then put them back into the water – at least 12 months.”
Mr Mueller said since blackfish need pristine water conditions, another complication in the wild comes from the amount of dirt entering the waterways.
“One of the major problems is sedimentation – the amount of sediment in the water,” he said.
“One of my bugbears is these dirt roads, especially where they follow and go across streams, they spew a lot of dirt up into the air and especially when trucks are moving around – that can cause a lot of trouble too.
“The dust doesn’t go and settle on the hills, it settles in the creeks.”
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