Salmon critics say fish farms should be on land. How it works for Murray cod

The Age

09-05-2025

The ponds at one of several aquaculture sites near Griffith are rectangles of murky green water fringed with reeds in a flat landscape of orange clay.
The pelicans perusing the perimeter and kites circling above see what the untrained human eye cannot – beneath a protective net, the water is teeming with Murray cod.
The ponds are part of the operations of Murray Cod Australia, trading as Aquna Sustainable Murray Cod. Chief executive Ross Anderson explains the colour of the water is by design – it's because the staff promote the growth of beneficial native algae.
Together with the water plants around the ponds' edges, the algae absorbs the nutrients from the fish poo and releases oxygen into the water by night. This results in less water usage and reduced need to mechanically oxygenate the water; an energy saving.
Another benefit: the algae creates a living culture that consumes other byproducts of the fish, preventing the build-up of chemical compounds that change the flavour of the fish.
'It's quite counter-intuitive, but from this muddy, green looking water, you get a clean, white-tasting fish,' Anderson says. 'Whereas in an artificial system in a tank … from that crystal clear water, you'll often end up with a muddy-tasting fish.'
While Anderson refrains from discussing the environmental woes facing the Tasmanian salmon industry, the contrasts are obvious.
Farmed salmon are fed ground-up wild fish – putting pressure on other ecosystems such as Antarctica – and antibiotics. Aquna feeds its Murray cod sustainable fish feed made from crops such as lupin, chickpeas and soybean and offcuts from chicken, beef and lamb – and their water quality control means they don't need to use antibiotics.
Salmon are farmed in open pens in the sea, releasing effluent into the water. In an unprecedented mortality event this summer, thousands of tonnes of dead salmon washed up on beaches in south-east Tasmania. Murray cod are farmed on land in ponds with no connection to natural waterways, using a relatively small amount of water from the Snowy Hydro scheme that later irrigates land including crops.
Salmon is threatening the critically endangered Maugean skate in Macquarie Harbour in western Tasmania. Aquna is helping state governments restock the vulnerable native Murray cod in the Murray-Darling basin.
The mass fish kill in Tasmania was caused by a bacterial outbreak against the backdrop of a marine heatwave, a problem that will probably recur as climate change worsens, unless the industry can adapt. Murray cod have evolved to withstand a wide range of temperatures and swings between drought and flood.
Aquna co-founder Mathew Ryan says he was drawn to aquaculture because the world needs to increase protein production using fewer resources, and specifically Murray cod because he wanted to stay in the Riverina and provide local jobs.
'Aquaculture was something that always fascinated me because the amount of production that you can get from a hectare of land [used for aquaculture] or from a megalitre of water is quite phenomenal,' Ryan says.
Murray cod is technically a perch but has an oily, white flesh like cod – I tried the Aquna product and found it had a delicate flavour and a satisfying meatiness. Some consumers are buying it instead of salmon, while in restaurants it competes with coral trout and Patagonian toothfish.
The company now has multiple properties near Griffith, with hatchlings in indoor tanks, juveniles in nursery ponds, and bigger fish in grow-out ponds. Anderson explains the fish have to be kept with others of the same size otherwise the bigger fish will eat or injure the smaller fish.
At the grow-out site with ponds dug out of the local clay soil, Ryan estimates 100-200 megalitres of water a year will produce 1000 tonnes of fish. By contrast, it takes 3800-4400 megalitres of water to produce 1000 tonnes of almonds, not including the shells, based on figures from the Almond Board of Australia and analysed by this masthead.
The company leans heavily into the sustainability of its operation in its pitch to consumers, marketing its product as fish 'for foodies who care where their fish comes from'. It does have the backing of the Australian Marine Conservation Society's GoodFish guide, which endorses farmed Murray cod from NSW and Victoria as well as farmed barramundi (but not wild caught) from all over Australia.
As the salmon industry grapples with social licence not just in Tasmania but around the world, many critics are calling for the fish to be farmed on land.
Industry group Salmon Tasmania has rejects this as fanciful, saying it would require too much land, water and energy and be five to 10 times more expensive. Independent aquaculture experts confirm there are significant logistical challenges.
'There is no single company with a major salmon farming initiative on land that is profitable, so it is, as yet, an undeveloped concept,' says Professor Tim Dempster, an expert in marine biology and aquaculture at Deakin University.
That's not the case for other species. Land-based aquaculture is the dominant form of fish farming globally, practised for centuries, especially in Asia. But is it more sustainable?
The main knock-on effect of farming salmon in the sea in Tasmania is the effluent that pollutes the marine environment. Dempster says New Zealand only avoids this problem because the industry is much smaller and more spread out.
In the salmon-producing countries of the northern hemisphere, such as Canada, Norway and Scotland, the main environmental concern is lice from farmed fish infecting wild salmon and reducing stocks, Dempster says.
Canada has decided to remove open-net salmon farming from British Columbia by June 2029 and told the industry it must transition to land-based systems.
Dempster doubts this will happen – he says the industry will probably move elsewhere.
Norway is experimenting with farming salmon onshore, but it is not a model for Tasmania because it is releasing the untreated seawater back out into the fjords, with the goal to direct the water to places where lice are least likely to infest wild fish.
There is also a fully self-contained approach – a 'recirculating aquaculture system' where the water is treated and reused. Atlantic Sapphire has spent $US1 billion ($1.55 billion) since 2011 pursuing this in Florida and is still bleeding money.
Farming salmon on land removes some environmental harms, but it is vastly more carbon intensive – both to build the tanks, and maintain the cool, clear water with high oxygen levels that salmon require.
Dempster says a salmon pen in the ocean in Tasmania might contain 50,000 cubic litres of water and produce 500 tonnes of fish. Salmon production in the state is 75,000 tonnes a year, according to Salmon Tasmania, so the volumes of water are vast.
Dempster says there are about 200 species globally that are farmed on land – mostly freshwater fish that can cope with lower water quality and higher temperatures, and don't require wild fish in their diet. (Marine fish need a source of Omega 3).
In Australia, there are several native fish that are suitable. Besides Murray cod there is the perennial pub favourite barramundi, which is both wild caught and farmed in tanks, ponds or occasionally the ocean, throughout Australia and Asia. Dempster says the environmental impacts are small.
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Globally, most land-based aquaculture around the world is done in tanks, and some of it is not environmentally sustainable at all.
'In some countries, say in China, where they are farming a lot of carp, they pour a lot of fertiliser in to fertilise those water bodies because the carp [eat plankton], and that then leads to that a lot of those nutrients exiting into the environment,' Dempster says.
'It depends on the species, the location and the farming system as to how good that system is for the environment.'