Abstract
Background:
Aeromonas hydrophila is an opportunistic pathogen that causes Motile Aeromonad Septicemia (MAS) with significant losses in Nile tilapia farms. Because of its bioactive compounds that enhance immunity and antioxidant capacity, dietary supplementation with fenugreek oil can effectively mitigate A. hydrophila- associated losses.

Aim:
This study aimed to explore the hematobiochemical, immune, antioxidant, and histopathological impacts of dietary fenugreek oil (FO) in Nile tilapia under normal culturing plus A. hydrophila infection.

Methods:
Approximately 300 Nile tilapia fingerlings (15.00 ± 3.00 g) were randomly distributed into five clusters, designated as FO-0 (control), FO-0.5, FO-1.0, FO-2.0, and FO-4.0 in which 0.0, 0.5, 1.0, 2.0, and 4.0 g FO/kg diet were supplemented, respectively. Diets were offered for 8 weeks at a 3% feeding rate. After 8 weeks of FO feeding, blood and tissue samples were collected to evaluate the impact of FO feeding under normal condition. Then, fish in each treatment were injected (intra-peritoneally) with 0.2 ml of A. hydrophila suspension and monitored for 2 weeks for any mortality. Then, blood and tissue were sampled.

Results:
Final body weight, gain, feed conversion ratio, specific growth rate, and protein efficiency ratio in, all FO-enriched groups displayed numerical increases relative to the control group (P > 0.05), peaking at 4.0 g FO/kg diet. FO dietary supplementation significantly improved antioxidant capacity, reflected by increases in superoxide dismutase and catalase activities with lowered malondialdehyde levels, particularly at 2.0-4.0 g FO/kg diet, both under normal and A. hydrophila challenge. Moreover, the innate immunity biomarkers lysozyme activity, and phagocytic activity and index exhibited marked dose-dependent improvements, both under normal and following A. hydrophila exposure (P < 0.05). Biochemically, total protein and globulin concentrations were significantly elevated with reduced urea concentration and hepatic enzymes activities in all FO-treated groups (P < 0.05). Moreover, all FO-supplemented groups showed improved histopathological features of the intestine, liver, and spleen with mitigation of the A. hydrophila-degenerative changes.

Conclusion:
Thus, FO could be used as a promising natural additive in Nile tilapia diet, particularly at 2.0-4.0 g/kg diet, to enhance hemato-biochemical profile, antioxidant defense, innate immunity, tissue integrity, and resistance against A. hydrophila, assuring sustainable and health-oriented aquaculture activities.

Key words: Nile tilapia; Antioxidant status; Innate immunity; Histopathological features; A. hydrophila.