Lice numbers slashed on fish bred for resistance
New research from salmon egg supplier AquaGen shows almost a halving of infestation in the second generation of fish genomically selected for resistance to salmon lice.
The Norwegian breeding company, which opened an office in Stirling earlier this year, has recently completed a study to document the effect of breeding for resistance to sea lice, with significant results.
"This is the third time our breeding strategy for resistance to salmon lice is verified under controlled lice infestation of salmon, and confirms that breeding for resistance to salmon lice provides a significant decrease in louse infestations," communications manager Anne Vik Mariussen told fishfarmingexpert's sister site, kyst.no.
High and low resistance
Mariussen said that in the last random test, conducted by VESO Vikan this year, salmon smolt from second-generation genomic selection were tested.
"Two groups of fish were genomically selected for respectively high and low resistance to lice. In addition, an unselected fish group served as control. All the fish went in the same tank and got infected twice."
After initial infection and lice counting, the fish were deloused with fresh water before being infected and the lice counted again.
Difference of 53 per cent
"Ten days after the first infection, results showed a difference in the number of lice between fish selected for high and low resistance of 53 per cent. Similarly, after the second infection, the difference between these groups was 55 per cent. The high-resistance group had respectively 40 per cent and 45 per cent fewer lice in the first and second infection compared to the unselected control."
The selection method used for the high-resistance salmon in this experiment is the same as that used for GEN-innOva® GAIN eggs.
This product was first supplied to farmers in autumn 2016 and is based on a combination of removal of lice collectors from the brood stock and second-generation genomic selection.
Wide margin
"At this point, we had trials that showed that this fish would get a reduced infestation of 30-40 per cent. Lice testing in 2017 confirms that we are able to reproduce the selection as planned by a wide margin," added Mariussen.
She pointed out that the ongoing field validation of GAIN fish in the sea will show how the strain performs under different farming conditions.
"For each salmon generation undergoing genomic selection again, lice resistance increases. There has been a reduction in infestation of 20-25 per cent for each new round of genomic selection. This gives great optimism for the future with regard to what can be achieved through breeding and genetics," said Mariussen.
Breeding technology
AquaGen has been working since 2010 to develop and adopt modern breeding technology in the fight against lice.
The first round of genomic selection for resistance to salmon lice was completed in 2013.
A breakthrough occurred in 2014 when an area of a gene - a quantitative trait locus or QTL - was identified that existed mainly in salmon that were very susceptible to sea lice, called the lice collector QTL.
"By removing brood that had this QTL, the offspring were less susceptible to lice. This roe was delivered to the farming industry for the first time in 2015. The effect of this lice collector-QTL is also verified in several commercial facilities."
In parallel with the search for QTLs, AquaGen systematically tested effects of genomic selection, which for many traits provides a more precise and more rapid genetic progress in comparison with traditional family-based selection.
