IPN- and PD-Resistance -Field Trial of QTL-Selection Based Stock

QTL-rogn2-250x145The first generation of Aqua Gens QTL-eggs, QTL-innOva™ have been followed in an extensive field trial benchmarking program. The results from freshwater sites, and for the S0-smolt followed until 90 days post transfer, show significantly higher IPN-resistance in the QTL-stock compared with the non QTL-stock. Results so far also show promising results when it comes to QTL-stock and PD-resistance.


Freshwater phase

Status freshwater stock, from eggs delivered in 2009/2010

This spring, the first generation of QTL-stock have finished their freshwater cycle. The status at 1st of May 2011 is one single IPN-diagnosis with mortality 0.16% measured over 90 days (in two tanks where IPN was diagnosed). For the non QTL-stock there were 6 IPN-diagnoses/IPN-outbreaks with mortality recorded with a range from 0.5% to 5.2%.

The number of positive IPN-diagnoses in farms that chose QTL-stock was reduced from 47% in 2009 (7 out of 15 freshwater sites) to only 7% (1 out of 15 sites) in 2010. In contrast for the non QTL-stock the number of positive IPN-diagnoses/IPN-outbreaks showed no reduction in 2010 with 43% (56 out of 14 sites)of the sites having IPN-diagnosed, compared to 36% in 2009 (figure 1).


Figure 1. Results from field investigation of QTL-stock in freshwater sites which previously have experienced losses due to IPN-outbreaks. The figure shows the accumulated number of IPN-outbreaks for the sites in 2010 compared to 2009 in hatcheries that received QTL-stock or non QTL- stock in 2010. In 2009 all the sites had non QTL-stock.


Sea water phase

S0 Status IPN, 2010

In August 2010 the first of the QTL-stock was transferred to sea as S0 smolts. A total of 9.8 million QTL-smolts and 6.1 million non QTL-smolts were transferred to 16 and 15 sea sites respectively. So far we have reports for mortality to 90 days post transfer representing 8.3 million QTL-smolts in 12 sites and 2.3 million non QTL-smolts in 7 sites.

Accumulated mortality to 90 days post transfer show average losses of 1.1% (range 0.6% to 3.0%) and 6.2% (range 0.2% to 32.9%) for the QTL smolt and non QTL-smolt respectively. One of the sites receiving non QTL-smolts experienced heavy losses, due to an IPN-outbreak. Almost 1/3 of the fish died during the outbreak, which began 5 weeks post transfer. So far there are no reports of IPN in the QTL-smolt (table 1).

Table 1.  Results from the field investigation of the S0, 2010. The table shows the number of smolts transferred, number of sea sites represented, average mortality first 90 days post transfer and diagnosed IPN +/-, for QTL-smolts and non QTL-smolts in 2010 and 2008 (non QTL-smolts).


S0 Status PD, 2010

Results from field trials (2007) and lab studies conducted in 2010 showed a positive correlation between IPN resistance and robustness against PD in the Aqua Gen strain. In other words, if the fish show high resistance against IPN, it also should be more robust to a SPDV infection. In Norway, the S0 would usually experience PD outbreaks during the period from April to June/July. Given this, most of the sites located in regions with a history of PD, should already have experienced the SPDV challenge.

Last autumn, 2.4 million QTL-smolts together with close to 1 million non QTL-smolts, were transferred to sites situated in areas normally affected by PD. The PD history for these sites show us that 3 out of 7 sites, that were stocked with S0 QTL-stock in 2010, experienced a PD outbreak in the non-QTL 2008 S0. For the sites holding non QTL-S0 stock in both 2010 and 2008, 2 out of 3 sites experienced an outbreak in the S0 2008. So far for the 2010 S0, none of the sites holding QTL-stock have experienced PD. For the sites holding non QTL-stock, one of the sites got a positive PD-diagnosis January this year (see table 2).

Given these positive observations on PD-robustness in the QTL-stock transferred as S0 2010, we look forward to follow the first groups of QTL-IPN/PD that will be transferred this autumn, as this product is a further improvement when it comes to PD-robustness.

Table 2.  Results from the field investigation of the S0 2010, in sites situated in areas normally affected by PD.  The table shows the number of smolts transferred, number of sea sites represented and diagnosed PD +/-, for QTL-smolts and non QTL-smolts in 2010 and 2008 (non QTL-smolts).



Further documentation of field performance

During this summer we will have the first result from the S1 QTL-smolt. Together with the reports from freshwater sites, where close to 120 million QTL-eggs have been delivered this season, this will make even more extensive documentation of the QTL-stock field performance. Results from further investigation of the field performance of the QTL-stock will be presented at Aqua Nor in Trondheim, Norway, 16th-19th August.