Search

Red sea bream iridovirus (RSIV) is an emerging viral pathogen having significant socio-economic and environmental impacts on marine and brackish aquaculture systems. The study documents certain interesting findings of an RSIV disease outbreak that caused 50% cumulative mortality among cage farmed Asian sea bass in India. The confirmatory diagnosis was made based on internationally approved protocols. The affected fish showed splenomegaly, anaemia, and abnormally enlarged cells within the spleen, liver, kidney, and brain. The consistent presence of two fish pathogens, viz., Vibrio alginolyticus and Vibrio fluvialis, in the liver, along with characteristic vibrio-induced pathologies were noted, indicating the possible role of these bacterial pathogens in RSIV pathogenesis during the outbreak. More strikingly, the surviving fish were found to carry the virus even after two months post-outbreak, warranting future investigations on the carrier status of RSIV survivors. Transmission electron microscopy in the survivors demonstrated atypical virus particles within the degenerated cells of the vital organs, suggesting the role of host immune response in preventing the maturation of RSIV particles in the survivors. Phylogram based on MCP and ATPase genes demonstrated the spread of the same RSIV clone across different countries, regardless of the fish species. Results also revealed the presence of two RSIV subtypes. Both subtypes were mainly distributed in marine demersal fishes of Asian countries. Presently, subtype 2 is the most frequently reported one. Subtype 1 revealed higher genetic diversity with a wider geographical spread and host range. Molecular analyses revealed that MCP and ATPase genes could be targeted in RSIV subtyping, with MCP as a better candidate. A purifying selection was observed on the MCP gene that can be applied for diagnostic protocols. In short, the study generates certain thought-provoking insights on RSIV through the analyses of a recent outbreak along with the genetic and epizootiological data of global strains. Further, the paper also forms the first report on the presence of RSIV in surviving fish post-disease outbreak in the absence of clinical signs. Altogether, the results highlight the necessity of strengthening quarantine and RSIV diagnostic measures to have sustainable aquaculture practices.

The relative abundance and biological characteristics of the spadenose shark Scoliodon laticaudus, from the south eastern Arabian Sea along Karnataka, India was studied. The average annual catch of the species during the period 2012–2017 was estimated at 112 t which formed about 13% of the total shark landing in the region. The species is landed mostly by trawl nets. Monthly abundance estimates showed that highest landing of the spadenose shark was observed in January. A total of 852 specimens were studied for biological characteristics. The length range of 19–63 cm was observed and length group of 45–55 cm formed the mainstay of the fishery. The length weight relationship for male and female and sexes pooled were 0.06588 L2.2386; 0.01118 L2.7497 and 0.01396 L2.6840 respectively. Analysis of covariance showed significant differences between the male and female ( p 0 . 05 ). In the present analysis, the regression co-efficient ( b value) for the species differs significantly from the value 3 indicating allometric growth. Lm50 for female and male were estimated as 32 and 33 cm. Chi-square-test on monthly sex ratio for the period showed that there was significant difference in sex ratio only in the months of January, October and November. S. laticaudus was found to be predominantly piscivorous in diet. The fishery is declining and efforts have to be taken for sustainable exploitation of resources.