First report on the diversity and distribution of parasitic monogenoids (Platyhelminthes) from catfishes (Siluriformes) in Arunachal Pradesh, India.

Monogenoidea (Platyhelminthes), one of the largest groups of ectoparasitic metazoans worldwide, comprises over 7000 nominal species distributed globally, many of which may represent a serious threat to their fish hosts in aquaculture conditions. The fish fauna of Arunachal Pradesh, India-a global hotspot of biodiversity-is reasonably well-documented, with at least 213 known species (including 69 Siluriformes). These faunas are an essential resource for this tribal state's economy. In sharp contrast, information on parasitic monogenoids of fish from the region is extremely limited, with only nine species described to date. In this study, 21 species of catfishes were collected and examined with the aim of expanding the current knowledge of the diversity and distribution of monogenoid species from Arunachal Pradesh. 15 (62.5%) of the 21 catfish species studied were infected with a total of 25 monogenoid species (11 previously described and 14 newly discovered in this study). Ten species of catfish were the first host records for new parasite species, while two species of catfish were new host records for previously known monogenoids. Arunachal Pradesh represents new geographic locality records for all 11 previously described parasite species, thus significantly expanding their distribution area from North and South India to extreme Northeast India. The patterns of parasite species richness in relation to three ecological traits (fish habitat, body size, and elevation) as well as host specificity across the 21 examined species of catfishes, the unique problem of too many parasite species in Wallago attu, and the future of parasitology in Arunachal Pradesh, India are discussed. © Indian Society for Parasitology 2021.