Dietary β‐Glucan From the Marine Diatom <i>Chaetoceros muelleri</i> Enhances Immune Responses and Resistance of Nile Tilapia to Tilapia Lake Virus Infection

This study evaluated the immunomodulatory effects of dietary β-glucan derived from the marine diatom Chaetoceros muelleri on immune responses and survival of Nile tilapia (Oreochromis niloticus) following Tilapia Lake Virus (TiLV) infection. Juvenile tilapias were fed diets supplemented with 0.1% or 0.2% β-glucan for 14 days prior to viral challenge. Fish were subsequently challenged with TiLV and immune-related gene expression was analysed in spleen and liver tissues. Fish fed the 0.1% β-glucan diet showed significantly lower cumulative mortality (26.67%) compared with the control group (55.56%) and the 0.2% group (42.22%). Dietary β-glucan significantly influenced the expression of multiple immune-related genes including cytolytic (NCCRP-1), stress-related gene (Hsp70), antimicrobial protein (C-lysozyme), cytokine (IL-8), pattern recognition receptors (TLR3, TLR5, TLR9), signalling adaptor (myD88), antiviral effector (Mx, RSAD-2), adaptive immunity (IgM, CD4). Correlation heatmap and gene co-expression network analyses revealed coordinated immune regulation, with Mx, RSAD-2 and CD4 acting as central hub genes associated with antiviral defence pathways. These results demonstrate that moderate dietary supplementation with C. muelleri-derived β-glucan enhances immune responses and improves resistance to TiLV infection in Nile tilapia, supporting its potential application as a functional feed additive in tilapia aquaculture.