Unravelling the ontogeny and tissue-specific expression profiles of immune-related genes in the near-threatened endemic catfish, Clarias dussumieri.

Clarias dussumieri, an air breathing catfish endemic to the Western Ghats in India, is categorized as 'Near Threatened' by the IUCN. This species is of high regional consumer demand and is one of the prioritized candidate species for aquaculture diversification and conservation. Despite its ecological and commercial significance, comprehensive studies on its immune system are lacking. This study elucidates the ontogenetic development and tissue-specific (brain, anterior kidney, gill, spleen, muscle, liver, hindgut and skin) expression profiles of key immune-related genes in C. dussumieri. Larvae were sampled at various developmental stages post-fertilization, and tissues from adult fish were analyzed for expression patterns of genes associated with inflammation (IL-1β, TNF-α, iNOS), antimicrobial defense (LYS, HAMP), stress response (HSP70), complement system (C3), cell-mediated immunity (MHC-IIβ, CD4-1), and adaptive immunity (IgM). The expression of IL-1β was highest at 60 days post-fertilization (60D), while TNF-α expression peaked at 25D before dropping notably by 60D. iNOS showed a peak at 7D, underscoring its importance in early immune defence. LYS exhibited a high expression at 10D, while HAMP peaked at 60D, highlighting their roles in antimicrobial defence. Stress marker HSP70 increased from 15D onwards and complement component C3 was consistently expressed at low levels throughout development. MHC-IIβ and CD4-1 showed significant increase since 10D and 7D respectively, suggesting the establishment of cell-mediated immunity. IgM expression increased notably from 15 days, indicating the development of adaptive immunity. In adult fish tissues, IL-1β, TNF-α, LYS and HSP70 showed highest expression in the hindgut, while C3 was predominantly expressed in the liver. MHC-IIβ and CD4-1 were highly expressed in the spleen and anterior kidney respectively. IgM was abundant in the anterior kidney and spleen. This study provides crucial baseline data on the immune competence of different developmental stages of C. dussumieri, informing strategies for effective vaccination and disease management in aquaculture, and enhancing our understanding of fish immunology for conservation efforts.