A viral agent implicated in the mortality of marine ornamental "Similar Damselfish" ( Allen, 1991) was isolated and characterized. The virus grew well in marine and freshwater fish cell lines from seabass and snakehead. The virus was sensitive to chloroform, acidic pH (3.0) and heat treatment at 56 °C. Biochemical characterisation indicated that the virus had double stranded DNA genome. Transmission electron microscopic analysis of ultrathin sections of infected cell pellets showed iridovirus-like icosahedral virus particles of 120-130 nm. Purified virus had six structural protein bands that ranged from of 44 to 132 kDa. PCR analysis confirmed the presence of viral DNA in infected cell cultures and sequence analysis of the major capsid protein gene showed an identity of 99.82% to that of largemouth bass virus. Serum neutralization studies involving the viral agent and koi ranavirus (KIRV) indicated partial homogeneity between the two isolates. Experimental infection of seabass () and similar damselfish () fingerlings with the similar damselfish virus showed cumulative mortalities of 68.75 and 93.33%. The biophysical and biochemical properties of the viral agent isolated, serological characteristics, size of major capsid proteins and the sequence similarity of the MCP gene proved that the virus belongs to the genus of the family. Ability of the virus to grow in marine and freshwater fish cell lines and its pathogenicity to one of the cultivable marine fish shows the wide host range of the virus. This is the first report of ranavirus induced mortality in marine fish in India.

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Background: Control of viral disease outbreaks in aquaculture and minimizing the loss of production can be achieved by development of effective vaccines. Efficacy of these vaccines can be improved by using adjuvants, immunostimulants or vaccine carriers. In this study, inactivated similar damselfish virus (SRDV) vaccine was prepared and expression profiles of immune related genes against virus challenge of the vaccine were investigated in seabass (Lates calcarifer). Methods: Formalin-inactivated virus vaccine was developed to assess its immune responses to SRDV challenge in fish. The immune response was induced by intra-peritoneal injection with inactivated viral vaccine added Quil-A® adjuvant. The transcriptional levels of immune genes IRF-7 and IL-10 were evaluated in the spleen and kidney of seabass from different groups by quantitative real-time RT-PCR assays. Result: Expression profiles of both genes (IRF-7 and IL-10) in the kidney and spleen of seabass immunized with vaccine added adjuvant were up-regulated at 48 hpi of the virus. In comparison, spleen of seabass immunized with vaccine added adjuvant showed highest expression profiles than kidney. The current study provides evidence for the presence of expression profiles of immune-related genes during the SRDV infection. The study also strongly suggests that Quil-A® adjuvant enhances the immune response of the vaccine candidates.

Aquaculture, being the fastest growing food production sector, has now become vital to the socioeconomic development of many countries. In India, aquaculture plays a significant role in food production, ensuring nutritional security, boosting agricultural exports, and generating job opportunities. The production of farmed fish has greatly expanded qualitatively and quantitatively in both freshwater and marine water regimes to fulfill the ever-growing demand. However, the occurrence of diseases is the main obstacle to sustainable aquaculture production, which has an impact on the socioeconomic status of fish farmers of the country. Viral diseases inflict irreparable damage to the aquaculture enterprise causing large-scale economic losses and ecological problems. Recently, there has been a spike in the incidence of new emerging viral diseases in diverse species of aquaculture species. Prophylactics by far being the only feasible method of viral disease control, the development of viral vaccines is highly imperative. A precise understanding of the disease pathology, etiological agent, and species susceptible to the specific diseases are highly essential in this perspective. The chapter highlights the emerging and reemerging viral diseases in the Indian aquaculture sector.

White spot syndrome virus (WSSV) is a pathogen causing significant economic losses to shrimp aquaculture worldwide. Previously, five genome sequences of the virus from farmed shrimp ( Penaeus vannamei and Penaeus monodon ) in India were reported, all originating from farms located on the east coast of the country. Here, we report three new and distinct WSSV genome sequences, two from shrimp ( P. vannamei ) farmed on the west coast of India and the third from the east coast.