RESISTANCE OF A RAINBOW-TROUT STRAIN TO INFECTIOUS PANCREATIC NECROSIS

Infectious pancreatic necrosis (IPN) is a well-known acute viral disea se of hatchery-reared salmonid fishes, but so far no effective treatme nt 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 commerc ial hatchery, was artificially challenged with IPN virus at 15-degrees -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 sensit ive 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 di fferences in mortality between the RT-201 and the RT-101 (positive con trol) were significantly different (P<0.005). Distribution of female f amilies 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 trans mittable and relatively stable. This interesting evidence underscores the importance of a genetic link-up of pathological investigations.