Curse May Be a Blessing

By Miller, Matthew

A noxious weed may provide a rich source of omega-3 oils to the aquaculture industry, according to Matthew Miller. Global production of farmed Atlantic salmon has grown from 55,000 tonnes in 1985 to more than 1.5 million tonnes in 2003. Its rapid expansion places an increasing demand on global supplies of wild fish that are harvested to provide protein and oil in aquafeeds.

The supply of seafood from fisheries is around 100 million tonnes per annum. This amount has not increased since the mid-1980s and will not increase in the future as most fisheries are at or above sustainable levels of production, and are prone to sharp periodic declines due to climatic factors such as El Nino. Fish oil stocks are also under increasing demand, not only from aquaculture but from the agriculture and biomedical industries.

Recently a gloomy picture of ocean and fish stock health emerged from estimates that all commercial fish and seafood species may collapse by 2048. The elimination of local populations of fish not only impairs the ability of marine ecosystems to feed a growing human population but also sabotages their stability and recovery potential in a rapidly changing marine environment.

Therefore the loss of biodiversity through selective overfishing could lead to a global collapse of all species currently fished. Aquaculture is thought to be a sustainable source of fish for this growing consumer demand, but as aquaculture uses wild fish for its diets it only adds pressure to fish stocks.

Omega-3 Oil

One of the major benefits of eating Atlantic salmon is that it contains high levels of omega-3 oil. Omega-3 fatty acids are important building blocks for our cell membranes, signalling pathways and neurological systems. They play a critical role in many functions in the body and are essential for good health, with benefits in heart disease, renal disease, rheumatoid arthritis, cancer, skin diseases and neurological diseases.

The Australian diet does not contain enough omega-3. Three- quarters of Australians consume less than one fish meal per week, and more than half the population consumes less than onesixteenth of the recommended daily intake.

One of the major misconceptions about fish is that they make omega 3. However fish, like humans, get omega3 from their diet.

Microalgae, microbes and single-cell marine organisms are the omega-3 factories of the ocean, and the “good oil” bioaccumulates up the food chain. Therefore the aquaculture industry must provide high amounts of omega3 to Atlantic salmon stocks through their diet.

Replacement oils for fish oil in aquaculture diets are being intensively researched to reduce the impact of aquaculture on wild fish stocks. Replacement oils have been sourced from a variety of commercial plant sources including sunflower, canola, olive, palm and linseed. The inclusion of these vegetable oils to replace part or all of the fish oil in fish diets resulted in good growth and health of the fish.

However, since these plant oils contain essentially no omega-3, fish fed these diets display reduced levels of omega-3, especially the important long chain omega-3 in eicosapentaenoic acid and docosahexaenoic acid.

Eating fish with reduced amounts of omega-3 is associated with reduced health benefits to the consumer compared with fish fed a diet high in fish oil containing greater levels of omega-3. Therefore, raising salmon on diets high in vegetable oil has the potential to dilute the important cardiovascular and other benefits associated with eating fish.

Patterson’s Curse

Patterson’s Curse was introduced to Australia in the 1880s, and is now a dominant pasture weed through much of NSW, the ACT, Victoria, South Australia and Tasmania. It also infests native grasslands, heathlands and woodlands.

Patterson’s Curse contains a unique biosynthetic precursor of omega-3 fatty acids. It also contains pyrrolizidine alkaloids that, when eaten in large quantities, reduce livestock weight or even cause death in severe cases. Therefore Patterson’s Curse is a m^jor concern and problem to the southern Australian farmer.

However, oil extracted from Patterson’s Curse has a potential role in the aquaculture industry as salmon can produce long chain omega-3 oils from the unique biosynthetic precursor it contains. In a trial conducted at the University of Tasmania in Launceston in association with the CSIRO Food Futures Flagship, fish fed Patterson’s Curse had similar levels of omega-3 compared with fish that were given omega-3 in their diet.

This finding was unique as it was the first time it has been shown that fish that were not directly fed omega-3 in their diet were able to maintain their levels of the “good oil”. Therefore oils such as those found in Patterson’s Curse, which contains this unique biosynthetic precursor, may be an environmentally friendly, renewable source of oil for aquaculture feeds.

This research has important implications for the aquaculture industry and environment. Patterson’s Curse could provide a renewable and sustainable source of oil while potentially reducing the amount of wild fish caught for aquafeeds. It could also maintain or in some cases increase the amount of omega-3 in salmon, and therefore increase the health of the consumer.

This result needs to be repeated on larger fish for a longer period of time to allow scientists to asses the long-term effects of feeding Patterson’s Curse to salmon and determine whether they maintain the biosynthesis of omega-3 over their whole life cycle. Other aquaculture species also need to be assessed to see if their omega-3 bioactivity is similar to that of Atlantic salmon.

At the moment there is no commercial source of Patterson’s Curse oil in Australia even though we have a bountiful supply of the plant. Before the aquaculture industry will consider using Patterson’s Curse it will need to be shown that it could supply a cheap and reliable source of this oil to meet the high demands of this industry.

Recently the CSIRO Food Futures Flagship’s omega-3 team has demonstrated that genetic modification of land plants can produce these omega-3 fatty acids in vegetable oils. These genetically modified plants may provide the most economically viable source of omega-3rich oil, not only for aquaculture but also for human consumption. Research in these areas has the potential for significant commercial, social and environmental benefits.

Patterson’s Curse may be a noxious weed, but it contains an important biochemical precursor that enables fish to produce their own omega-3 oils.

Matthew Miller is a PhD student at the University of Tasmania’s School of Aquaculture, and is supported by the CSIRO Food Futures Flagship at CSIRO’s Marine and Atmospheric Research Laboratories, Hobart.

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