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The first complete picture of wild Atlantic salmon gut bacteria has just been published, paving the way for a more ecologically sustainable salmon farming industry.

Last week, researcher Dr Martin Llewellyn (Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow) and co-workers in Ireland, Scotland, Canada, USA and Wales took a first step towards understanding the key role of salmon gut bacteria in salmon health (

After two years intensive sampling from adult salmon feeding grounds in West Greenland, returning adults and freshwater juvenile salmon in Canada and Ireland, they have developed the first compete picture of wild Atlantic salmon gut bacterial diversity across the distribution of the species.

The data show that bacterial community composition within the gut was not significantly impacted by geography. Instead life-cycle stage (parr, smolt, adult) strongly defined both the diversity and identity of gut microbial assemblages in the gut, with evidence for community destabilisation in migratory phases. Amongst other observations, Mycoplasmas were recovered in all life-cycle stages in huge abundance, suggesting a potentially vital role for this class of bacteria for gut health.

Dr Llewellyn’s data pave the way for fundamental research in this field, including the development of probiotics, pre-biotics and even whole artificial bacterial communities to improve farmed salmon health and reduce the impact of salmon aquaculture on wild fish stocks.

Dr Llewellyn told Fish Farming Expert: “Atlantic salmon farming now supports a multi-billion dollar industry worldwide. In Scotland the Atlantic salmon aquaculture industry has a £1.4 billion turnover, supports 8000 jobs and predicts 30% growth by 2020.

“Scottish expansion is unsustainable given the current reliance on over-exploited wild fish stocks as a primary ingredient is salmon feed, and poor growth efficiency on alternative plant-based feeds. This situation presents many new challenges to both fish and farmer.

“Efficient digestion and absorbance of nutrients in food relies heavily on the bacteria present in our intestines – our so-called ‘microbiome’ – in humans as well as especially our herbivorous cousins (such as cows, horses, sheep). It is also increasingly apparent that good ‘gut health’ (ie healthy microbiomes) has wider links with everything from depression to cancer.

“As the industry attempts to move farmed Atlantic salmon (carnivores in the wild) to more ecologically sustainable plant-based feeds, understanding the role of their gut bacteria becomes a vital consideration”.