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Remarkably high levels of resistance to pancreas disease (PD) have been recorded in unvaccinated Land catch fish, reared on a Norwegian farm, next to vaccinated stock from a local source which suffered severe PD-inflicted losses.
Mortalities in the unvaccinated stock were less than five per cent compared to losses of between 15 per cent and 40 per cent in the vaccinated fish. Land catch Natural Selection (LNS), the Scottish international salmon breeding company who supplied the unvaccinated stock to a farm at Hordaland, Western Norway, have placed molts in equally challenging PD environments in other areas of Norway over the last three years and each time have shown impressively high levels of resistance to infection and very low, or indeed no, resultant mortalities.
“This is the first time we’ve been able to give concrete mortality and survival percentages in the face of what was a severe PD attack,” said Alan Stewart, Business Development Director, Land catch, “although previous studies in Ireland have indicated similar resistance.
Molts were introduced to the farm in autumn 2008, alongside PD vaccinated molts from another source. Once they’d settled, they showed typically good growth patterns. During the following summer (2009), when the fish were averaging 2kg, and thus of very considerable economic value, PD struck the whole area.
“The fact that the Land catch fish had not been vaccinated helped to ensure that any differential in mortality between the two stocks demonstrated the value of genetic enhancement alone, and was unrelated to vaccination. The results were remarkable with the Land catch molts incurring losses of between two per cent and five per cent while the vaccinated fish suffered mortalities of between 12 per cent and 44 per cent.”
As a consequence of these field observations, LNS is now collaborating with the world renowned Roslin Institute, Edinburgh, and with Dr David Graham of the Northern Ireland Veterinary Institute, where the PD virus was first isolated, to define the exact nature of the genetic resistance. It’s expected this will allow the identification of one or more quantitative trait loci (QTL) that correlate with the high levels of resistance, observed in the Landcatch stock.
“This will allow PD resistance to be added to the range of specific selection factors which we take into account as part of our individual broodstock fish selections,” said Alan Stewart. “In addition, if this is possible, it will increase the level of inherent genetic resistance to PD at every subsequent generation of our three-year breeding cycle.
“Even this year, however, the commercial eggs and molts which we are now releasing are derived from the families with the same genetically enhanced resistance to viral disease, observed in the Land catch stocks at Hartland.
“While it would be wrong, obviously, to claim that PD has been conquered, our field data to date indicates that using Land catch stock can be expected to significantly reduce losses from this scourge.”
