Viral Nervous Necrosis (VNN) in
red snapper
Intro
Clinical signs
Diagnosis
Factors
Treatment and preventions
Special characteristics
Also seen in older fishes
Mode of transmission
Mainly affect juvenile and larvae
caused by red-spotted grouper nervous necrosis virus (RGNNV), from genus Betanodavirus (family: Nodaviridae)
Virus (Betanodavirus)
Disease
RNA 1 encodes viral replicase, RNA2 encodes teh capsid protein
Can survive for 1 year in the right environmental conditions
Contain two genetic segments, RNA1 and RNA2
Selective breeding to NNV resistance
Good management practices
Vaccination
Stressors
High stocking densities
Improper handling
High ambient temperature
Virulence of particular betanodavirus strain
Horizontal transmission
Vertical transmission
Persist clinically in infected live fish
Clinical signs
Change in colouration is important indication
High mortalities
Gross pathological signs
Microscopic pathological signs
Behavioural abnormalities
RGNNV
Distributed in various warm water fish (eg: grouper, red snapper)
Optimal growth temperature (25C - 30C)
Abnormal swimming (erratic swimming)
Loss of equilibrium
Anorexia
Blindness
Overinflated swim bladder
Abrasions
Intracytoplasmic inclusions in brain tissues
Vacuolation of central nervous tissues, incuding retina
Colour change
Hyperactivity
RT-PCR
Indirect serological methods (ELISA test)
Histology
Apply Biosecurity in the aquaculture system
Direct contact with infected fish
References
Zorriehzahra, M. J., Adel, M., Dadar, M., Ullah, S., & Ghasemi, M. (2019). Viral nervous necrosis (VNN) an emerging disease caused by Nodaviridae in aquatic hosts: Diagnosis, control and prevention: A review. In Iranian Journal of Fisheries Sciences (Vol. 18, Issue 1, pp. 30–47). Iranian Fisheries Research Organization. https://doi.org/10.22092/ijfs.2018.117849
Viral Encephalopathy and Retinopathy | Disease guide | The Fish Site. (n.d.). Retrieved November 24, 2020, from https://thefishsite.com/disease-guide/viral-encephalopathy-and-retinopathy
Doan, Q. K., Vandeputte, M., Chatain, B., Morin, T., & Allal, F. (2017). Viral encephalopathy and retinopathy in aquaculture: a review. In Journal of Fish Diseases (Vol. 40, Issue 5, pp. 717–742). Blackwell Publishing Ltd. https://doi.org/10.1111/jfd.1254