6.1. Introduction 6.2. Aetiology of VNN 6.3. Host range 6.4. Collection and shipment of fish samples for detection of NNV 6.4.1. Samples preservation for viral isolation in cell culture 6.4.2. Samples preservation for molecular diagnosis and typing 6.4.3. Samples preservation for serological diagnosis 6.4.4. Samples preservation for histology and immunohistochemistry 6.5. Diagnostic procedures for NNV 6.5.1. Preparation of samples for examination 6.5.2. Real-time RT-PCR 6.5.3. Sequencing 6.5.4. Virological examination 6.5.4.1. Cell cultures and media 6.5.4.2. Incubation and inoculation of cell monolayers 6.5.4.3. Subcultivation procedures 6.5.4.4. Procedure for titration to verify the susceptibility of the cell cultures to infection 6.5.5. Virus identification 6.5.6. Indirect Fluorescent Antibody Test 6.5.7. Histology 6.5.8. Immunohistochemistry IHC (avidin-biotin-peroxidase technique) 6.5.9. Conservation of samples References