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Validating in vitro feed trials

9 December 2020, at 10:00am

An in vitro modelling device that simulates the digestive system of a salmon, allowing researchers to assess the digestibility of feed ingredients without as many costly feed trials, has been validated by the results of two recent studies.

The team behind SalmoSim: Raminta Kaslauskaite, Joseph Humble and Martin Llewelyn
The team behind SalmoSim: Raminta Kaslauskaite, Joseph Humble and Martin Llewelyn

© SalmoSim

SalmoSim, which has been developed by researchers at the University of Glasgow, replicates the conditions inside the digestive tract of an Atlantic salmon. The device has been developed to allow companies to assess the impact of various feed ingredients without the expense of using live fish. While it may not be perfect, it can enable companies to perform pre-screening of ingredients prior to launching full-scale feed trials – thereby saving both time and money.

The makers of the model have just signed their first commercial contract with Calysta, manufacturer of Feedkind, an animal-free protein source for use in aquaculture, to support their research and development.

“Feed trials can cost over £100,000 each to run. So it’s important to ensure that the ingredients being used are viable options. By running a range of ingredients through our SalmoSim in vitro gut model, we can swiftly assess which are the most promising,” explains Raminta Kaslauskaite, who helped to develop the device and has recently written up a number of successful trials involving it.

Comparison with live salmon

The first trial involved comparing how two diets – one containing fishmeal and one without – affected the bacterial communities both within live salmon and in SalmoSim.

“Real salmon and SalmoSim responded similarly to the introduction of the novel feed, with most taxa of microbes (96 percent of the microbes in the salmon and 97 percent of the microbes in SalmoSim) unaffected, while a subset of taxa was affected non-identically across both systems. This shows that SalmoSim is a valid in vitro gut system that can be used as a tool for the improvement of salmon nutrition,” says Kaslauskaite.

Pre-biotics

The second trials involved using SalmoSim to assess the impact of mannose-oligosaccharide (MOS) pre-biotics – which are currently widely deployed in animal agriculture as immunomodulators as well as to enhance growth and gut health.

A prebiotic called Bio-MOS is being considered for use as growth promotor in salmonid aquaculture. However, before a full-scale in vivo trial was conducted, Kaslauskaite, modified SalmoSim to evaluate the impact of the prebiotic on host microbial communities.

In biological triplicate, microbial communities were stabilised in SalmoSim followed by 20-day exposure to the pre-biotic, then an eight-day wash-out period.

The results suggested that MOS could indeed have an effective prebiotic impact, resulting in a significant increase in formate (p=0.001), propionate (p=0.037) and isovalerate (p=0.024) levels, correlated with increased abundances of several principally anaerobic microbial genera (Fusobacteria, Agarivorans, Pseudoalteromonas, Myroides). They also help to further validate SalmoSim as a means of assessing microbiome modulators.

“In conjunction with previous in vivo studies linking enhanced VFA production alongside MOS supplementation to host growth and performance, our data suggest that Bio-MOS may be of value in salmonid production. Furthermore, our data highlight the potential role of in vitro gut models to augment in vivo trials of microbiome modulators,” Kaslauskaite concludes.

What's next?

As well as supporting studies that explore the impact of different feed ingredients, pre- and probiotics on the gut microbiota, the SalmoSim team have now modified their device to deliver rapid-turn-around, low-cost information on digestibility.

Senior editor at The Fish Site

Rob Fletcher has been writing about aquaculture since 2007, as editor of Fish Farmer, Fish Farming Expert and The Fish Site. He has an MA in history from the University of Edinburgh and an MSc in sustainable aquaculture from the University of St Andrews. He currently lives and works in Scotland.

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