Enhancing immune and antioxidant responses in Nile tilapia through dietary supplementation with Ulva fasciata extract: A study on gene expression and resistance to Aeromonas hydrophila

Abstract Background : The study focused on the impact of Ulva fasciata extract (UFE) supplementation in the diets of Nile tilapia ( Oreochromis niloticus ) on blood and biochemical markers, immune and oxidative responses, and the expression of related genes, with a specific interest in their condition following exposure to Aeromonas hydrophila . Methods : Four different levels of UFE were tested in the diets: 0% (0 mg kg − 1 ) for the control group (U0), and incremental additions of 0.05% (50 mg kg −1 ), 0.1% (100 mg kg −1 ), and 0.15% (150 mg kg −1 ) for the experimental groups U50, U100, and U150 respectively. Groups of 45 fish weighing 3.126 ± 0.120 g were fed these diets over 90 days. Results : The study found that groups treated with UFE showed statistically significant enhancements ( p < 0.05) compared to the control group. These improvements included increased red and white blood cell counts, higher haemoglobin concentrations, greater packed cell volume, and elevated enzyme activities—specifically, superoxide dismutase, catalase, alanine aminotransferase, and aspartate aminotransferase. Additionally, lysozyme and phagocytic activities were notably higher, especially in the U100 group after exposure. Before exposure to Aeromonas hydrophila , all levels of UFE supplementation led to increased expression of TNF‐α and COXII genes and decreased NFκ‐B expression. After the challenge, UFE intake resulted in varied expression levels of immune and antioxidant genes (TNF‐α, NFκ‐B, SOD, and COXII) in the liver, with the most effective responses observed in the U50, U100, and U150 groups. Conclusions : The findings underscore the potential of dietary UFE as a natural antioxidant and immune booster for Nile tilapia.