Plant‐Derived Treatments for Monogenean Parasites in Farmed Fish: A Systematic Review and Meta‐Analysis

ABSTRACT Monogeneans are among the most problematic ectoparasites in finfish aquaculture. Plant‐derived compounds have been widely explored as therapeutic agents, yet their efficacy and safety have not been quantitatively synthesized across studies. This study provides a meta‐analysis of plant‐based treatments against monogeneans, integrating 453 in vitro and 262 in vivo treatment comparisons from 50 publications. Random‐effects and multilevel models were used to estimate pooled efficacy, assess heterogeneity, and evaluate patterns across compound types, concentration categories, and exposure durations. Safety was assessed using therapeutic indices or margins of safety derived from acute‐toxicity endpoints. Most studies focused on dactylogyrids and gyrodactylids infecting two freshwater fish species. Plant‐derived treatments produced consistently strong antiparasitic activity in vitro and in vivo (overall parasite‐load reduction ~75%–80%), although with substantial methodological heterogeneity. Isolated compounds were the only group achieving high mortality at low concentrations and short exposures, whereas crude extracts and essential oils generally required higher concentrations or longer treatments. Safety outcomes showed no consistent relationship with concentration, and only 18% of treatments achieved complete parasite elimination while remaining safe for fish. Notably, some studies recommended treatment regimens even when their results did not clearly support strong therapeutic performance, highlighting the need for more explicit standards for defining effective and safe therapies. Overall, plant‐derived compounds show promise for managing monogenean infections, but strong efficacy does not guarantee practical or safe application. Integrating in silico approaches, combining ligand‐based screening with parasite‐specific molecular targets, offers a promising route to prioritize candidates with genuine therapeutic potential in aquaculture.