The study of the outbreak of Viral Hemorrhagic Septicemia in rainbow trout fish farms during 2014-2018 from Chaharmahal va Bakhtiari, Lorestan and Isfahan Provinces

Viral Hemorrhagic Septicemia is one of the most important infectious diseases of cultured fish, causing mass mortality, especially in rainbow trout. This study aimed to investigate the occurrence and pathological lesions of VHS in Chahrmahal va Bakhtiari, Lorestan, and Isfahan Provinces, between 2014 and 2018. The virus was identified using the RT-PCR method in clinically suspected fish. According to the obtained results, 202 samples (13.33%) of 1515 studied samples were infected with Viral Hemorrhagic Septicemia Virus. The infection rates during the study were 14.65% in Chaharmahal va Bakhtiari, 15.16% in Lorestan, and 8.5% in Isfahan Provinces. Comparison of the infection rate in fish with different weights indicated that the highest level of infection was in the fish weighing above 200 g (28.22%). The infection rate in fish with 5-200 g and 1-50 g weight was 19.44 and 8.6%, respectively. Considering that the disease has been fluctuating in the range of 9-19% during the study, full-scale and drastic actions are necessary for eradicating Viral Hemorrhagic Septicemia.