Nr. 2 /2013
Pancreas Disease (PD), caused by Salmonid alphavirus (SAV), has for many years been one of the most costly diseases affecting Norwegian salmon farming. Producers and the authorities have implemented a number of structural and operational measures with the aim of limiting losses from this disease. In addition different vaccines against PD have been developed as well as different types of special feed.
On behalf of the Norwegian Seafood Federation (FHL) the Norwegian Veterinary Institute carried out a major analysis (2011) where a number of different measures were evaluated for the effect they have had to limit the scope and prevalence of PD (PD-free project). The analysis was based on operational, health and harvest data from a total of 202 smolt inputs during the period 2007-2009. The two main parameters that showed significantly reduced risk for PD outbreaks and influenced the severity of the outbreaks were (i) Vaccination against PD and (ii) Avoidance of IPN outbreaks during the production cycle. There is reason to believe that the widespread use of PD-vaccination in endemic zones, combined with a significant reduction in the number of outbreaks of IPN has contributed significantly to the positive development of the PD situation, as registered during the most recent period(Figure 1).
Development of QTL-innOva-IPN/PD Ever since 2005, breeding for increased resistance against PD has been central to our R&D programme at AquaGen. In the period 2006-2008 a large scale field trial was carried out, in which 395 families were transferred for PD challenge under natural field conditions. AquaGen has utilised data from both the preliminary field trial and various follow-up laboratory challengetests, to identify and document the genetic markers that have efficacy against PD. These markers are not as clear and strong as IPN-QTL, but combined, they could significantly increase PD-resistance of fish. Our analysis also showed that among the three strongest QTL’s associated with PD protection we find the IPNQTL. Based on the findings of QTL searches and subsequent documentation from laboratory infection trials (Figure 2), the product QTL -innOva IPN/PD was launched in the market in the egg-season 2010/11.
Field documentation set-up
The first fish produced from QTLinnOva IPN/PD eggs were transferred to sea in the autumn of 2011. To be able to evaluate the effect of these eggs in the field we have closely followed up fish at a total of 19 locations, comprised of 8 locations in autumn 2011, 3 locations in spring 2012 and 8 locations in autumn 2013 (table 1). All of these locations were in the area from Rugsund in Bremanger to Hardanger fjord where historically there has been a high infectious pressure from SAV.
Of the 19 locations involved in the field documentation, 15 had previously experienced clinical outbreaks. All of the fish that were in the field trial were also PD vaccinated.
Results from field documentation
The results from the field documentation are presented in figure 3, 4 and 5. Following there is a brief summary of each smolt transfer.
A total of 8 sites with 3 million fish transferred in autumn of 2011 were followed-up from stocking to harvest. Of the 8 sites, 7 had experienced clinical PD outbreaks in the previous intake. PD was detected at 3 of the sites and an average accumulated loss from transfer to harvest for these sites was 13.2%. Average accumulated losses for all 8 sites, from stocking to harvest was 7%. There was no evidence of IPN in any of the sites that were monitored.
A total of 3 sites, all with previous PD outbreaks, in total 1.3 million fish were transferred and followed up with respect to PD. Accumulated losses for all 3 sites from stocking to the end of June 2013 are 9.8%.
To date there hasn’t been any diagnosis of IPN or PD on any of the sites (14-15 months post-stocking).
In total, 8 sites with 3.4 million fish stocked and followed up with respect to PD. Of these sites, 5 had PD outbreaks in the previous production cycle. By the end of June 2013, 1 of these sites had a diagnosis of PD. Accumulated mortality for this site from intake to the end of June is at 1%. Accumulated losses for all of the 8 transfers up until the end of June is at 1.1% (8-11 months post transfer). By the end of June there hasn’t been any diagnosis of IPN or PD at any of the other locations.
Reduction in PD outbreaks
Both PD and IPN, two of the most costly diseases of the last 10-15 years are in marked decline in Norwegian aquaculture. We believe that this clear trend of a reduction, in the region of 40% in the number of PD diagnoses in the first half of 2013, when compared to the first half of 2012 was positively related to a large reduction in IPN that has occurred since 2010.
Combined with a PD vaccine that has a moderate but significant effect, it has contributed to a “virtuous circle” with a gradual reduction in the number of affected populations and a commensurate gradual reduction of the infection pressure in the environment. Based on efficacy data from both laboratory and field trials it is reasonable to expect that the situation going forward will improve as of the autumn 2013 transfers, which represent the first stocking that will have a significant proportion of fish based on QTL-innOva IPN/PD.
To produce eggs that are strong against PD, we must use several markers, each with a moderate effect (under 20%) and combine these with families of salmon that we previously found to be strong against PD in field trials.
This compares with production of IPN-strong eggs which uses only one marker with very high effect (responsible for over 80% of variation in survival at IPN challenge). For IPN eggs this means that we have a direct measure of whether the fish is strongly resistant or not (marker + or -). For PD eggs we cannot rely on just one marker. It follows that the selection of fish with the correct attribute will be less precise at the individual level, but will be good at the group level.