Immune-Modulatory Effects of Ethanolic Plant Extracts: A Systematic Review and Meta-Analysis of Specific Plant-Parts Responses

Abstract The rise of antibiotic resistance and increasing environmental concerns have accelerated the demand for effective, sustainable alternatives to conventional therapeutics in aquaculture. Medicinal plants have emerged as promising candidates due to their diverse bioactive compounds, which exhibit strong immunomodulatory and antioxidant properties. However, the biological efficacy of plant-based interventions varies greatly depending on the specific plant part utilized. This meta-analysis systematically evaluated the differential effects of ethanol-extracted plant parts—roots, leaves, fruits, flowers, stems, and whole plants—on key immune and antioxidant markers in fish. Thirty peer-reviewed studies were included, with a combined sample size exceeding 8,000 fish. Immune-related outcomes such as white blood cell (WBC) count and lysozyme activity, as well as oxidative stress biomarkers including superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA), were analysed. The results demonstrated that leaf and root extracts were the most effective in enhancing immune responses and antioxidant enzyme activities, significantly upregulating SOD and CAT while reducing MDA levels. Notably, leaf extracts showed superior efficacy in increasing lysozyme activity and WBC counts. Conversely, fruit extracts were associated with increased MDA, indicating potential pro-oxidant effects. Subgroup analyses confirmed significant heterogeneity based on plant part, highlighting the need for selective use. This review confirms that the choice of plant part critically determines the health-promoting effects of medicinal plants in fish. The main conclusion from this review is that leaf and root extracts represent the most reliable plant parts for enhancing immune function and oxidative stability in aquaculture species.