Immune and metabolic mechanisms underlying fishmeal replacement with Tenebrio molitor in enhancing Pseudobagrus ussuriensis resistance to Aeromonas veronii

Fishmeal, the predominant protein source in aquaculture, is increasingly constrained by resource depletion and price volatility, posing challenges to the sustainability of the industry. Tenebrio molitor , rich in high-quality protein and immunologically active compounds, represents a promising alternative. However, its role in modulating fish immunity and metabolism remains poorly characterized. In this study, juvenile Pseudobagrus ussuriensis were fed diets containing 0 %, 10 %, 20 %, or 30 % T. molitor for 90 days, followed by an Aeromonas veronii challenge. Liver tissues were sampled at 0, 24, and 48 h post-infection for histological, biochemical, and transcriptomic analyses. H&E staining indicated that higher dietary inclusion of T. molitor effectively alleviated liver damage. ELISA results showed increased activities of immune effector enzymes (ACP, ALP, LZM) with infection time and replacement ratio, whereas antioxidant indicators (SOD, CAT, T-AOC) decreased and MDA levels increased, suggesting that immune activation may be accompanied by oxidative stress. Transcriptomic profiling identified 830 and 68 differentially expressed genes in the 30 % group compared to the 0 % group at 24 and 48 h, respectively. Antigen processing and presentation pathways were significantly enriched at both time points. STEM analysis revealed persistent activation of Jak–STAT and AGE–RAGE signaling pathways, along with dynamic changes in lipid and porphyrin metabolism linked to energy homeostasis and inflammatory responses. WGCNA demonstrated that both replacement level and infection time co-regulated gene modules associated with immune and metabolic functions. RT–qPCR validation corroborated the transcriptomic findings. Collectively, these findings indicate that dietary supplementation with T. molitor enhances immune function in P. ussuriensis , underscoring its potential as a sustainable alternative to fishmeal. The coordination between immune and metabolic pathways provides mechanistic insights and practical guidance for developing efficient and environmentally sustainable protein sources in aquaculture. • First study on the effects of Tenebrio molitor as a fishmeal replacement on Pseudobagrus ussuriensis under bacterial infection. • Dietary Tenebrio molitor reduces liver damage from Aeromonas veronii and boosts immune effector enzyme activity. • Transcriptomics shows antigen processing/presentation and JAK-STAT pathways play key roles in immune and metabolic regulation. • Provides molecular insights and practical guidance for using insect protein as a sustainable fishmeal alternative in aquaculture.