Abstract

Background:
Nile tilapia (Oreochromis niloticus) production faces persistent threat from Aeromonas hydrophila, the causative agent of Motile Aeromonas Septicemia, whose virulence is substantially amplified under thermal stress. Antibiotic-dependent disease management has accelerated multidrug resistance, necessitating sustainable non-pharmacological alternatives. Although Moringa oleifera leaf powder and Spirulina individually demonstrate immunomodulatory and antibacterial properties in fish, their combined application alongside short-term fasting under simultaneous thermal and infectious challenge has not been investigated.

Aim:
This study aimed to evaluate the effect of combined M. oleifera leaf powder and Spirulina dietary supplementation, with short-term fasting, on gill histopathological integrity and A. hydrophila colonisation in Nile tilapia subjected to heat stress and bacterial immersion challenge

Methods:
Sixty fish were distributed into four groups: negative control (C-), positive control (C+)vsubjected to heat stress at 34°C and immersion challenge at 10⁷ CFU/mL A. hydrophila, herbal supplementation with prior fasting (T1), and herbal supplementation without fasting (T2). Secondary lamellar hyperplasia and degeneration/necrosis were scored on H&E-stained sections; gill A. hydrophila colonies were enumerated on RS agar.

Results:
Both T1 and T2 significantly reduced histopathological scores and bacterial counts compared with C+ (P < 0.05). T1 achieved the greatest tissue protection, with lesion scores comparable to C⁻, whereas T2 showed intermediate but significant improvement. Bacterial counts in T1 and T2 were significantly lower than in C+ and did not differ significantly from each other.

Conclusion:
Combined M. oleifera and Spirulina dietary supplementation significantly attenuated gill histopathological damage and reduced A. hydrophila burden in heat-stressed Nile tilapia. Short-term fasting augmented the protective effect of herbal supplementation, with the combined regimen yielding gill integrity comparable to uninfected fish. This integrative nutritional approach represents a promising antibiotic-free strategy for disease prevention in intensive tilapia aquaculture.

Key words: Aeromonas hydrophila; Fasting; Moringa oleifera; Spirulina; Tilapia.