A COST-EFFECTIVE process of breeding “super” salmon that have a natural built-in resistance to the scourge of sea lice is being developed by a Scottish research consortium.

The technique will allow salmon producers to bypass previously expensive and complex methods of using DNA or genetic markers to identify which fish can best resist sea lice.

Instead, producers would use a much simpler approach to select the most suitable parent fish for breeding programmes.

It is hoped the project, led by Dr Smaragda Tsairidou and Professor Ross Houston at the University of Edinburgh’s Roslin Institute, will enhance fish health and wellbeing by improving stocks’ resistance to sea lice and could be extended to cover other health issues, such as gill disease.

Sea lice are a major problem across Scotland’s farmed salmon industry, with parasites from open net farms blamed for a slump in wild salmon numbers to their lowest level since records began.

The parasites thrive in cramped cages and feed on the mucus, skin and blood of fish, resulting in fish being virtually “eaten alive”.

There are also concerns the medicines given to farmed fish to ward off infestations of sea lice have also had

an impact on wild stocks of salmon and trout.

Selective breeding using genomic tools to establish which salmon display in-built natural resistance to sea lice normally involves gathering information on tens of thousands of DNA sequences, or genetic markers.

The process can be particularly expensive in traditional aquaculture settings. Using a scientific technique called genotype imputation, the researchers have developed a lower-cost method that could make the process feasible for more breeders and producers.

The approach uses a smaller number of genetic marers to predict the resistance of salmon to sea lice. This looks for variations at specific positions in the genes of fish that indicate how it will respond to parasites and disease.

The information then allows breeders to select parent fish with improved resistance to sea lice.

Similar techniques have been used successfully in livestock breeding programmes and could be effective in other aquaculture species, including shrimp and tilapia.

The process could also be used as a preventative measure to improve other important health traits, such

as resistance to gill disease.

Meanwhile, gill disorders can be caused by the growth of micro-organisms in the water such as plankton and algae.

The researchers worked in collaboration with Hendrix Genetics and the University of Stirling?s Institute of Aquaculture as part of a project supported by the Scottish Aquaculture Innovation Centre (SAIC).

Professor Ross Houston, chairman

of aquaculture genetics at the Roslin Institute, said: "Sea lice is one of the costliest health-related problems for

the global salmon industry and can have a wide-scale impact on salmon health and welfare.

?In this study we used low density genetic markers to predict the resistance of salmon to sea lice. This is potentially a more cost-efficient way of breeding salmon with improved resistance to parasites and other diseases, helping to improve animal welfare and production."

Scotland has more than 200 salmon farms, which produce 170,000 tons of fish a year. Concerns about the scale of sea lice problems recently prompted the introduction of new rules that require the farmed salmon industry to report weekly levels of sea lice.

The Scottish Salmon Producers Organisation, however, has maintained farm operators have made progress in the fight against sea lice, with levels recently said to be at their lowest in six years.

The industry has introduced a range of counter meamsures aimed at preventing and controlling lice infestations, including hydrolicers and thermolicers, which use water rather than chemicals in medicines to clear affected fish.

Net pens with skirts, semi-closed containment systems that prevent lice copepodites from finding salmon and “cleaner” fish that eat the lice from infected salmon have also been used, while some researchers are working on lice vaccines.

Caroline Griffin, aquaculture innovation manager at SAIC, said: “Collaborative research projects are crucial for finding new methods for enhancing fish health and wellbeing, while also supporting the future sustainability of the industry.

“Sea lice continues to be a prominent challenge for the sector worldwide and developing cost-effective, data-led techniques for future breeding could transform the ways in which we manage and treat sea lice on fish farms.”