Nr.1 / 2012
The first generation of QTL-IPN fish from Aqua Gen has now been followed throughout the entire production cycle. The results show that the prevalence and extent of IPN in both fresh water and sea water were either eliminated or significantly reduced in comparison to previous generations and reference groups that did not possess the QTL-IPN. This positive trend is confirmed by official statistics on the number of registered IPN outbreaks in the Norwegian fish farming industry. It is expected that the increased frequency of IPN resistant QTL fish, combined with reduced infection pressure in the environment will further improve the disease situation and reduce losses in the coming years, resulting in improvements for both animal welfare and profitability in the fish farming sector.
Aqua Gen introduced the first QTL-IPN eggs in autumn 2009 to the Norwegian market. In the 2009/10 season a total of 45 million QTL eggs were delivered to customers that historically had experienced major challenges with IPN in both fresh water and sea water. This represented about 12 % of the entire Norwegian egg intake in that season. Based on the positive field results from this year-class, Aqua Gen has seen a significant increase in demand for QTL eggs in the European market.
Nearly 350 million QTL eggs from Aqua Gen have been delivered to Norwegian hatcheries in the last 3 years. With 170 million QTL eggs in the season 2011/12, the percentage of QTL eggs of the total year-class has risen to nearly 50 %. This growing proportion of IPN resistant fish in the salmon industry has contributed to a positive trend of reducing registered IPN outbreaks and increasing survival throughout the production cycle.
Reduction in IPN outbreaks
According to the Norwegian Veterinary Institute’s official statistics, the number of recorded outbreaks of IPN in the salmon industry has reduced from 221 outbreaks in 2009 to 149 outbreaks in 2011. This represents a reduction of 33 % on a national scale over the past 2 years.
The first groups of QTL fish from Aqua Gen have now been through the entire production cycle from egg to harvest. In this information letter, we will summarize the results from those groups we have followed through fresh water (egg intake 2009/10) and sea water (smolt transferred to sea autumn 2010 and spring 2011) and which have been through the most critical phase for IPN.
Results in fresh water
In the period from November 2009 to May 2010, we followed 15 fresh water sites that stocked a total of 29.1 million QTL eggs. These sites that participated in the field investigation had historically experienced significant losses due to IPN. Of the 15 sites which stocked QTL eggs this season, none experienced clinical outbreaks of IPN in the fresh water phase. One site was diagnosed with IPN virus, but with negligible mortality (0.2 %).
We also established a reference group, consisting of 14 sites that received a total of 23.1 million standard eggs. These were sites that did not have the same very serious IPN histories as those in the experimental groups, and therefore were not directly comparable. Among the sites within this reference group there were diagnoses of IPN on 6 out of 14 sites, with mortality rates at the group level which ranged from 0.5 to 7.0 %. Sites with standard eggs had the same level of IPN as the previous season. The results are summarized in table 1.
Results in sea water
For the sea water phase, we followed two smolt groups, autumn 2010 (5.6 million fish in 11 sites) and spring 2011 (11.4 million fish in 14 sites). As with the fresh water survey, we established reference groups on sites that used standard smolt only (table 2 and 3).
S0, autumn 2010
For fish of QTL origin transferred as smolts in autumn 2010 there were no diagnoses of IPN. Average mortality recorded to 90 days after transfer was 1.1 %. For the reference group IPN was found on one site and the average mortality recorded to 90 days after transfer at the 7 sites was 6.4 %. The results are summarized in table 2.
S1, spring 2011
For QTL fish transferred in spring 2011, IPN was diagnosed at 3 out of 14 sites. Average mortality recorded to 90 days after transfer at 14 sites was 4.6 %. In the IPN positive sites mortality varied from 5 to 9 %. The clinical picture of the 3 cases was complex, with both smolt quality and bacterial infection contributing to mortality. In the 12 reference sites, IPN outbreaks were recorded at 7 sites, and the average mortality recorded to 90 days post sea transfer was 12.7 %. In the IPN positive sites, mortality varied from 3.2 to 38.0 %. The results are summarized in table 3.
Testing of QTL status at IPN occurrence
In collaboration with the fish health service and personnel at the QTL farms that experienced IPN outbreaks, we implemented a test program for analyzing the QTL status of fish that died /survived the outbreaks. The fish were tested both for the presence of the IPN virus and to see if they had the marker for IPN resistance.
The results from the testing showed that the majority of fish that died of IPN did not have the correct QTL status, meaning that they lacked the marker for IPN resistance. The frequency of fish with the incorrect QTL status in these groups was in the range of 2 to 8 %. This is probably a result of errors in the test methodology used to genotype the broodstock from Aqua Gen. Although this type of analysis can never be 100 % accurate, we have now improved the analytical method and quality-assurance work on further genotyping and as a result subsequent selection of broodstock is now more precise.
The first harvest results
The first S0 group of QTL fish transferred to sea 2010 were harvested in October 2011, 13 months after sea transfer. This was part of a group, farmed in the county of Nordland in Northern Norway of approximately 600,000 fish. The result from stocking shows that over 95.8 % of the fish transferred to sea reached a market size of at least 4.5 kilograms, with a superior rate of 96.8 % and a biological and
economic feed conversion of 1.03 and 1.04 respectively. Although this probably is not representative of all groups in the field experiment, such results and feedback are inspiring, and strengthens us in the belief that we as geneticists and egg supplier are a significant contributor to the success of future development of the aquaculture industry.