Detection of betanodavirus in wild golden grey mullet (Chelon aurata) in southern parts of the Caspian Sea using Real-time RT-PCR and immunohistochemistry

Viral Nervous Necrosis (VNN), caused by betabodavirus, is considered as one of the most important threats for mariculture and aquaculture globally. The disease was previously reported in wild golden grey mullet (Chelon aurata) from the Caspian Sea in 2004. To update these findings and to examine the phylogenetic relationship of the betanodavirus involved in disease outbreaks in Iran with other betanodavirus genotypes, forty golden grey mullets were screened for the presence of betanodavirus using real-time RT-PCR targeting the T4 region of RNA2 coat protein gene. The results showed that all 40 fish has positive test for the virus, which was also confirmed by immunohistochemistry. The phylogenetic relationship of betanodavirus involved in disease outbreaks in Iran from 2016 to 2017 was compared with betanodavirus genotypes sequenced from elsewhere, and the 300 bp product from the real-time RT-PCR sequenced was found to have a 98–100% homology with red-spotted grouper nervous necrosis virus (RGNVV), confirming that the betanodavirus detected in wild golden grey mullet in the southern parts of the Caspian Sea adjacent to Iran determined to be the RGNNV genotype.