Information Letter

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Nr. 1 / 2009

Eyed eggs from the Aqua Gen population of Rainbow Trout stripped in 2009 are the first generation with parents selected for increased resistance for IPN. Using selective breeding to reduce the extend of the disease is new within commercial breeding programs.

The prevalence of IPN in Rainbow Trout

Systematic breeding for improved resistance to IPN (Infectious Pancreatic Necrosis) in Atlantic salmon has been performed by Aqua Gen since 2001. After three generations a considerable selection response has been achieved for this trait.

In Norway, a total of 14 IPN outbreaks were reported in Rainbow Trout stocks in 2008. Twelve of these were reported to be in fresh water (National Veterinary Institute). From August 2008 IPN is no longer a notifiable disease, and this may affect the number of outbreaks reported. For Chile, no statistics are available that shows the prevalence of the disease, but we do know that the virus is most problematic from the first feeding up to about five grams.

Increased resources invested in breeding

Since 2006 Aqua Gen has increased the use of resources in the Rainbow Trout breeding program. Number of traits recorded has increased and three separately bred populations have been crossed into one breeding population (breeding nucleus) using the same model as for Atlantic salmon. The advantages of this amalgamation of three populations to one are increased selection intensity and reduced variation for the customer from year to year. Together with the crossing of the three existing populations an additional strain (Strain B) has also been included in the testing.

IPN challenge test

200 families of first fed fry (0.2 grams) were challenged with IPN virus in separate tanks (Fig. 1). At the end of the test the accumulated mortality was 26.5 %. The average mortality between families ranged from 0 to 87 %.

Figure 1. IPN challenge testing of 200 families in separate tanks.

Three families were randomly chosen to be tested in four replicates each (Table 1). As shown in Table 1 different families showed stable results, indicating a good repeatability of the test.

Table 1. Mortality (%) after
IPN challenge test in the four replicates
of three randomly chosen families.

Figure 2. Variation in mortality between the different crossings in the IPN challenge test. AG03= Aqua Gen population first fed 2003, AG02= Aqua Gen population first fed 2002, AG01= Aqua Gen population first fed 2001, AG00= population first fed 2000, Strain B= strain from an external breeding program.

PDF of the Information Letter is found here