Occurrence and host associations of Dollfustrema bagarii (Digenea: Bucephalidae) in channel catfish cage culture in Northern Vietnam.

A survey was conducted across 11 provinces in Northern Vietnam to investigate the distribution of Dollfustrema bagarii metacercariae - a causative agent of significant losses in cultured channel catfish (Ictalurus punctatus) - and to identify its first intermediate host. A total of 337 fish specimens were collected from 103 farms. Metacercariae of D. bagarii were detected in 72 farms (69.9% of farms), and 44.51% of the sampled fish were positive. The prevalence in lowland provinces was 3.14 times higher than that in mountainous regions (p < 0.001), while no significant difference was observed between fish cultured in reservoir/lake and those in river (p = 0.634). We identified the golden mussel Limnoperna fortunei (Bivalvia: Mytilidae) as the first intermediate host of D. bagarii. The morphological characteristics of its daughter sporocyst and cercariae were described, and the identification was confirmed through comparison of 28 S rDNA sequences with those of D. bagarii.