The study looks into the cause deaths of Puntius sarana in cage aquaculture at Maithan reservoir, Jharkhand, India. The infected fish exhibited symptoms as loss of appetite, lethargy, scale loss, bleeding and sores on their belly. Pathogens from the gut were identified as Lactococcus garvieae using morphological and biochemical tests, molecular work viz, 16S rRNA PCR sequencing and phylogenetic analysis. Microbiological tests confirmed that L. garvieae was linked to the disease outbreak and deaths in the fish species. The findings were further supported by survival assays, biofilm formation and swimming motility assay. The strain showed resistance to several antibiotics, including streptomycin, enrofloxacin, ciprofloxacin, and tetracycline indicating multi-drug resistance. Histopathological assessment revealed significant damage to tissue architecture in liver, kidney and gill of L. garvieae infected P. sarana. To gain a better insight into the immunocompromised conditions of the fish and the host-pathogen interactions, qPCR assays were done to study the relative changes in the patterns of gene expression of immune-related genes. The transcriptional profiling of bacterium infected fish tissues (i.e., liver, kidney and gill) showed statistically significant differences in the expression patterns of genes related to antioxidant activity and immune-related gene as compared to the control fish. The present study will serve as a basis for risk assessment and developing management strategies to reduce the harmful effects of the pathogenic bacterium, L. garvieae. Furthermore, it may provide practical guidelines for fish farmers to implement preventive strategies aimed at disease control.
Keywords: Disease outbreak, cage culture, P. sarana, L. garvieae and emerging pathogen