Short-term fasting enhances the resistance of common carp (Cyprinus carpio) to Aeromonas hydrophila: Impacts on gut microbiota, glucose, and oxidative stress.

Abstract

Background and aim: Aeromonas hydrophila is a significant pathogen in freshwater aquaculture, contributing to high morbidity and mortality in common carp (Cyprinus carpio). Conventional reliance on antibiotics raises concerns about resistance and environmental impact. This study aimed to evaluate the effects of short-term fasting (1 or 2 days) on physiological, oxidative stress, and microbial responses in C. carpio infected with A. hydrophila.

Materials and methods: Sixty C. carpio were divided into four groups (n = 15): negative control (uninfected), positive control (infected), T₁ (1-day fasting + infected), and T₂ (2-day fasting + infected). Infections were induced by immersion in an A. hydrophila suspension (10⁸ colony-forming units [CFU]/mL). Three days post-infection, blood was collected for glucose and hemoglobin analysis. Malondialdehyde (MDA) levels in head kidney tissue were assessed as a marker of oxidative stress. Gut samples were analyzed for lactic acid bacteria (LAB) through standard plate counts. Statistical comparisons were made using a one-way analysis of variance and Kruskal-Wallis tests (p < 0.05).

Results: The T₂ group (2-day fasting) exhibited significantly better physiological responses than T₁ and the positive control. Blood glucose levels in T₂ (83.5 ± 1.71 mg/dL) were significantly lower than the positive control (127 ± 3.85 mg/dL), but within the normal range. Hemoglobin levels were highest in T₂ (7.8 ± 0.27 g/dL), indicating preserved oxygen-carrying capacity. MDA levels, though not statistically different, were lowest in T₂ (14.42 ± 0.60 mg/L), suggesting reduced oxidative stress. LAB counts were highest in T₂ (1.69 × 10⁹ CFU/g), indicating improved gut microbiota balance.

Conclusion: A 2-day fasting regimen enhanced disease resistance in C. carpio by modulating glucose metabolism, preserving hematological integrity, reducing oxidative stress, and enriching beneficial gut microbiota. These findings support short-term fasting as a promising non-pharmacological strategy for managing bacterial infections in aquaculture, with the potential to reduce antibiotic dependence.