Plant Immunostimulants Against Aeromonas hydrophila in Freshwater Fish: Efficacy, Dose, and Mechanisms

Abstract

Aeromonas hydrophila remains an important bacterial aquaculture, while recurrent antibiotic use raises concerns about resistance, residues, and ecological pressure. This systematic review evaluated the efficacy, dose, administration route, and plausible mechanisms of plant-derived immunostimulants used to protect freshwater fish against experimental A. hydrophila challenge. Searches covered PubMed, Crossref/DOI pages, Google Scholar, Garuda, and official journal portals for studies published from 1 January 2021 to 15 July 2026. Eligible studies were primary in vivo experiments reporting a defined botanical intervention, dose, challenge protocol, and health or survival outcome. Eighteen studies were included in a qualitative synthesis. Most interventions improved at least one innate immune, antioxidant, growth, histological, or survival endpoint; however, responses were strongly influenced by plant identity, extraction method, dose, exposure duration, fish species, and challenge design. The most reproducible preventive dietary range was 0.1–1.0% of feed for concentrated extracts or essential oils, commonly administered for two to eight weeks. Potent extracts were effective at 100–200 mg kg−1 feed, whereas crude or fermented leaf materials often required 50–100 g kg−1 feed. Immersion treatments were promising at 0.25–0.50% or approximately 500 mg L−1, but evidence was less extensive. Mechanisms converged on direct antibacterial activity, activation of lysozyme, complement, phagocytosis and respiratory burst, regulation of inflammatory genes, antioxidant protection, and mucosal or microbiota modulation. Evidence quality was limited by weak phytochemical standardization, heterogeneous challenge models, infrequent blinding, and incomplete reporting of adverse effects and uncertainty. Plant immunostimulants are promising preventive adjuncts, but commercial recommendations require standardized preparations, dose-response trials, and multi-farm validation.

Keywords: Aeromonas hydrophila, Disease resistance, Freshwater aquaculture, Medicinal plants, Phytobiotics