Global Burden of Clinostomum complanatum in Freshwater Fish: A Systematic Review and Meta-Analysis of Prevalence and Pathological Effect

Abstract

Clinostomum complanatum infection is a trematode parasite infecting diverse freshwater fish hosts, causing pathological damage and economic losses. Despite its veterinary and public health importance, its global burden remains insufficiently quantified. This study aimed to assess the global burden of C. complanatum infection in fish, focusing on prevalence, habitat associations and pathological impacts. A systematic review and meta-analysis were conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. Literature published from database inception to 7 June 2025 was searched. Thirty studies involving 70 freshwater fish species from 18 families were included. Pooled prevalence estimates were calculated using random-effects models in R software. Heterogeneity was assessed using Cochran's Q and I² statistics, whereas subgroup analyses and Egger's regression test were performed to evaluate variability and publication bias. The prevalence of C. complanatum varied markedly among fish species, reaching 100% in Squalidus chankaensis but remaining undetected in species such as Cobitis biwae, Hypomesus transpacificus, Salangichthys microdon and Silurus asotus. The pooled global prevalence was 28.7% (95% confidence interval [CI]: 22.0%–36.5%), with substantial heterogeneity (I² = 99.0%). Significant variation was observed across fish families, geographic regions and habitat types. The highest prevalence occurred in Percidae (97%), Osphronemidae (67%) and Gobionidae (65%). Regionally, Africa (49%) and Europe (46%) showed the highest prevalence. Infection rates were higher in aquaculture systems (45%) than in natural habitats. Metacercariae predominantly encyst in muscle, buccal and branchial tissues, producing yellow grub cysts associated with muscle degeneration and inflammatory responses. The internal transcribed spacer (ITS) region was the most frequently used molecular marker, although molecular diagnostic approaches remained limited overall. C. complanatum is a widespread and heterogeneous threat to freshwater fish health. Standardized surveillance, greater use of molecular diagnostics and targeted control strategies, particularly in aquaculture systems, are essential to reduce infection burden, economic losses and potential zoonotic risks.