Abstract

Infectious pancreatic necrosis (IPN) is a well-known acute viral disease of hatchery-reared salmonid fishes, but so far no effective treatment for IPN has been developed. This report is of a strain (RT-201) of rainbow trout resistant to IPN. The strain, which evolved in a commercial hatchery, was artificially challenged with IPN virus at 15°C for 28 days. The population was tested totally 20 times throughout 1979-1989 and the average (±standard deviation) mortality was 4.3±5.7% whereas in the positive controls (RT-101 strain, highly sensitive to IPN) it was 96.1±5.5%. In the 5th generation of an isolate of RT-210 reared at a public station without any pathogens there was 5.0% mortality and in the positive control (RT-101) it was 100%. The differences in mortality between the RT-201 and the RT-101 (positive control) were significantly different (P<0.005). Distribution of female families of the population with various levels of mortality to an IPNV challenge was 7.6±7.4% (n=22, range 0-23%). The results indicate that the resistance manifested in strain RT-201 was genetically transmittable and relatively stable. This interesting evidence underscores the importance of a genetic link-up of pathological investigations.