Ashoktaru Barat*

ABSTRACT

The snow trout (Schizothorax richardsonii), native to the high-altitude Himalayan region, thrives across a broad thermal range (0-27°C). It serves as an excellent model species for investigating the responses of cold-water fish to both abiotic and biotic stressors. In this study, we conducted a comparative analysis of liver transcriptomes from Schizothorax richardsonii challenged with Aeromonas hydrophilla (Ah+) and those mock-challenged (Ar-). The species' transcriptome database was established through RNA sequencing (2×100 bp paired end) using the Illumina 2000 sequencing platform. Among the 50,453 unigenes assembled de novo, 24,464 were annotated, including 82 associated with immune response genes. We identified 265 differentially expressed unigenes (189 upregulated and 75 downregulated) in the Ah+ group compared to the Ah- group. The majority of these genes involved in immune regulation during bacterial pathogenesis were associated with extracellular regions, membrane integrity, ion binding, signal transduction, antigen processing and presentation, and MHC class I protein complexes. Notably, 15 unigenes associated with immune response and 9 related to signal transduction gene ontology terms showed significant dysregulation in the bacterial-challenged group. Four immune genes—Interleukin 1?1, prostaglandin-endoperoxide synthase 2a & 2b, and ankyrin repeat domain—exhibited high activity against A. hydrophilla. This study offers initial insights into potential molecular changes occurring in this model fish species during pathogenic infestations.