Molecular characterization of three digeneans parasitizing marine fish in the Gulf of Thailand

The Gulf of Thailand is a highly diverse marine ecosystem, yet knowledge of its helminth fauna remains fragmentary. Marine fishes were obtained in 2024 from accidental catches of crab-trap fishers or captured by local fishermen using boats in Chumphon Province, Thailand. In this study, we molecularly characterize three digenean trematode genera parasitizing marine fishes from this area: <i>Lecithocladium</i> (Hemiuridae) from the short mackerel (<i>Rastrelliger brachysoma</i>), with a prevalence of 77% in 22 fishes and ten worms examined for morphology; <i>Prodistomum</i> (Lepocreadiidae) from <i>R.brachysoma</i>, with a prevalence of 18% in 22 fishes, and from <i>Rastrelliger kanagurta</i>, with a prevalence of 100% in one fish, with 10 worms examined for morphology; and <i>Lepocreadioides</i> (Lepocreadiidae) from the double-lined tonguesole (<i>Paraplagusia bilineata</i>), with a prevalence of 75% in four fishes, and eight worms examined for morphology. Sequences of nuclear ribosomal markers (18S, ITS2, and 28S) were generated, providing the first molecular data for <i>Lepocreadioides orientalis</i>. Our analyses confirm the presence of <i>Lecithocladium angustiovum</i> and <i>Prodistomum</i> sp. in the Gulf of Thailand, contribute new molecular data, and provide a morphological description of <i>Prodistomum</i> sp. Despite the Gulf of Thailand's high ichthyofaunal diversity, its helminth communities remain insufficiently investigated, highlighting the need for future research.