Digenetic trematodes represent one of the most ecologically significant groups of helminth parasites affecting freshwater fishes, with implications for biodiversity, aquaculture productivity, and zoonotic health. The present study investigated the prevalence, morphological diversity, molecular identity, and phylogenetic relationships of trematodes infecting freshwater fishes in the Azamgarh district of Uttar Pradesh, India. Systematic sampling was conducted across six sites representing diverse hydro-ecological habitats of the Ghaghara River system. A total of 642 fish specimens belonging to Channa punctata, Clarias batrachus, and Heteropneustesfossilis were examined seasonally for one year. Overall prevalence of trematode infection was 54.8%, with peak levels recorded during the monsoon season. Morphological characterization revealed species such as Clinostomumcomplanatum, Allocreadiumhandiai, Maseniavittatusi, and Opisthorchis sp. Histopathological analyses confirmed significant tissue damage in gills, intestine, and liver of infected hosts. Molecular characterization using ITS1 and COI gene markers validated morphological identifications and revealed >97% similarity with global Gen Bank entries. Phylogenetic analyses clustered Indian isolates with their respective families, with evidence of host-associated haplotypes and possible cryptic diversity. The study highlights the ecological, pathological, and public health relevance of trematode infections and underscores the need for integrated monitoring in Indian freshwater ecosystems.
Kumar et al. (Wed,) studied this question.