SELECTION OF RAINBOW-TROUT RESISTANT TO VIRAL HEMORRHAGIC SEPTICEMIA VIRUS AND TRANSMISSION OF RESISTANCE BY GYNOGENESIS

In 1984 a programme of selection for resistance to viral haemorrhagic septicaemia virus (VHSV) in rainbow trout was initiated. The progenies of 14 males were submitted to a VHSV waterborne challenge. The mortal ity ranged from 30 to 95% and the heritability of resistance was estim ated to be 0.63 +/- .0.26. One male consistently provided the most res istant offspring, and the second generation was produced from sires an d dams selected among these families. The mean resistance improved and several females giving birth to resistant offspring were identified ( 0-10% mortality while the mortality in the controls was from 70 to 90% ). The meiotic gynogenetic progeny of these females also demonstrated high resistance (mortality less than 10%). The role of superficial tis sues in the resistance was confirmed and there was a striking differen ce in the growth of VHSV in fins excised and infected in vitro. The fi ns from resistant fish replicated the virus poorly as compared with th e fins of susceptible fish.