Fish viral diseases are significant in aquaculture and fisheries, leading to substantial economic losses globally.
1. Infectious Hematopoietic Necrosis (IHN)
- Causative Agent: Infectious hematopoietic necrosis virus (IHNV)
- Family: Rhabdoviridae
- Genus: Novirhabdovirus
- Transmission: Horizontal (via waterborne virus or direct contact).
- Replication Cycle: Typical RNA virus replication in the cytoplasm.
- Pathogenesis: Virus targets hematopoietic tissues and endothelium.
- Clinical Signs
- Darkening of skin, exophthalmia, abdominal distension.
- Hemorrhages in internal organs and tissues.
- Control
- Biosecurity, water disinfection, and vaccination (inactivated or DNA-based vaccines).
2. Viral Hemorrhagic Septicemia (VHS)
- Causative Agent: Viral hemorrhagic septicemia virus (VHSV)
- Family: Rhabdoviridae
- Genus: Novirhabdovirus
- Transmission: Horizontal (waterborne, infected fish, or carrier species).
- Replication Cycle: Similar to IHNV.
- Pathogenesis: Infection causes endothelial cell damage, leading to hemorrhages.
- Clinical Signs
- Petechial hemorrhages, ascites, anemia, and abnormal swimming behavior.
- Control
- Avoid stress, disinfect water, and use certified virus-free stock.
3. Infectious Pancreatic Necrosis (IPN)
- Causative Agent: Infectious pancreatic necrosis virus (IPNV)
- Family: Birnaviridae
- Genus: Aquabirnavirus
- Transmission: Horizontal and vertical (via eggs).
- Replication Cycle: Occurs in the cytoplasm of infected cells.
- Pathogenesis: Virus causes necrosis in pancreatic and gastrointestinal tissues.
- Clinical Signs
- Anorexia, corkscrew swimming, pale organs, and liquefied pancreas.
- Control
- Hygienic broodstock handling, vaccination, and water sterilization.
4. Spring Viremia of Carp (SVC)
- Causative Agent: Spring viremia of carp virus (SVCV)
- Family: Rhabdoviridae
- Genus: Vesiculovirus
- Transmission: Horizontal (contaminated water and vectors like leeches).
- Replication Cycle: Cytoplasmic replication typical of rhabdoviruses.
- Pathogenesis: Targets vascular and hematopoietic tissues, causing viremia.
- Clinical Signs
- Lethargy, hemorrhages, ascites, and exophthalmia.
- Control
- Strict biosecurity, quarantine, and vaccination where available.
5. Koi Herpesvirus Disease (KHVD)
- Causative Agent: Koi herpesvirus (KHV)
- Family: Alloherpesviridae
- Genus: Cyprinivirus
- Transmission: Horizontal (waterborne, direct contact) and carrier fish.
- Replication Cycle: Typical DNA virus replication in the nucleus.
- Pathogenesis: Targets gills, skin, and kidney tissue.
- Clinical Signs
- Gill necrosis, skin lesions, and high mortality in koi and common carp.
- Control
- Temperature regulation, biosecurity, and vaccination.
6. Epizootic Hematopoietic Necrosis (EHN)
- Causative Agent: Epizootic hematopoietic necrosis virus (EHNV)
- Family: Iridoviridae
- Genus: Ranavirus
- Transmission: Horizontal (waterborne, contact with infected tissues).
- Replication Cycle: Cytoplasmic replication typical of iridoviruses.
- Pathogenesis: Affects hematopoietic and endothelial cells.
- Clinical Signs
- Pale gills, hemorrhages, and swollen spleen.
- Control
- Quarantine, water treatment, and strict hygiene protocols.
7. Lymphocystis Disease
- Causative Agent: Lymphocystis disease virus (LCDV)
- Family: Iridoviridae
- Genus: Lymphocystivirus
- Transmission: Direct contact or waterborne transmission.
- Replication Cycle: Cytoplasmic replication.
- Pathogenesis: Affects fibroblasts, causing hypertrophic lesions.
- Clinical Signs
- Wart-like nodules on skin and fins.
- Control
- Isolation, improved water quality, and no effective vaccines.
General Control Measures for Viral Fish Diseases
- Hygiene and Biosecurity
- Disinfection of equipment, tanks, and water systems.
- Avoiding overcrowding in aquaculture setups.
- Health Certification
- Use certified virus-free broodstock and fry.
- Quarantine
- Isolate newly introduced or suspected fish populations.
- Vaccination
- Effective for some viral diseases like IHNV and VHS.
- Monitoring and Early Detection
- Regular health checks and lab testing.
- Euthanasia and Disposal
- Humane euthanasia of heavily infected populations to limit spread.
By implementing these measures, viral disease outbreaks in aquaculture can be minimized, ensuring healthier fish populations and sustainable aquaculture practices.