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Fertilisation of coho salmon eggs with milt from a SRS-resistant male. Photo: AquaGen
Fertilisation of coho salmon eggs with milt from a SRS-resistant male. Photo: AquaGen

A collaboration between researchers in Chile and Norway, directed by the AquaGen company Blue Genomics Chile, has resulted in a breakthrough in breeding for SRS resistance in coho salmon, AquaGen states.

The discovery of a major QTL (part of the genome that has been shown to influence a quantitative trait) for SRS resistance has already been implemented in AquaGen Chile’s egg production. This gives expectations of a significantly reduced infection pressure of SRS in the environment and consequently less need for antibiotic treatment, says the Norway-based firm.

Chile is the global leader in coho farming, with a total production of 130,000 tons annually, representing 18 per cent of Chilean salmon farming output. Production of coho in Chile has advantages over Atlantic salmon and rainbow trout. Coho have the fastest growth rates, lowest time to harvest and the lowest feed conversion rates. The attractive meat colour also gives the product a significant market in Japan as well as in emerging markets.

Immune to lice

The coho is immune to lice and ISA, but is highly susceptible to the bacterial disease SRS (Salmon Rickettsial Syndrome), also known as piscirickettsiosis. The bacteria are prevalent in all the farmed salmonid species in Chile, causing substantial economic losses and animal welfare problems. Treatments with antibiotics lowers losses from outbreaks, but the industry is trying to reduce the

SRS-resistant coho salmon should reduce Chile's use of antibiotics. Photo: AquaGen.
SRS-resistant coho salmon should reduce Chile's use of antibiotics. Photo: AquaGen.

use of antibiotics and is considering alternative control strategies.

In 2016, 382 tons of antimicrobials were used for salmon production, 700 times more than Norway, which used 523kg.

For coho, SRS is responsible for 80 per cent of losses from infectious disease and for most of the need for antibiotic treatments.

Over the last three years AquaGen has consolidated coho breeding in Chile by the merger of three previous breeding programs. The company claims the joint qualities of these programs, together with increased investment in modern breeding technology, should result in considerable progress for coho salmon production.

High inheritance to resistance

AquaGen says analysis of data from several infection tests has shown high inheritance for SRS resistance. A very significant QTL has been found that explains 46 per cent of the genetic variation in SRS resistance in the coho. Close to 60 per cent of fish having two copies of the beneficial variant of the QTL survived a challenge, whereas fewer than 10 per cent of the fish without the QTL survived.

"The 13 million coho eggs produced using QTL-selection in 2017 will have considerably improved resistance to SRS," says AquaGen in a statement. "This way the Chilean industry will help establish selection for improved SRS resistance that can support the ongoing efforts to reduce the use of antibiotics in the Chilean salmon industry."

AquaGen says the breakthrough was possible because of close scientific and technical collaboration between Fundación Chile, ADL Diagnostics, FAVET-Inbiogen Lab. (Veterinary Faculty) at the Universidad de Chile by Dr. Victor Martinez, CIGENE at the Norwegian University of Life Sciences (NMBU), Affymetrics, AquaGen and Blue Genomics Chile. The research was financially supported by the Chilean funding institutions CORFO and FONDEF-IDEA, as well as AquaGen and Blue Genomics Chile.