S Singh, D C Kritsky, C Hahn, S Prakash, A Tripathi
This study aimed to (1) assess the diversity of Gyrodactylus species infecting Day's mystus, Mystus bleekeri (Siluriformes: Bagridae), in northern India; (2) provide genetic resources for two new species to support taxonomy, phylogeny, and diagnostics; and (3) compile an annotated checklist of Gyrodactylus species from Indian freshwater fishes. Between 2022 and 2025, two new species, Gyrodactylus octoacanthicus n. sp. and Gyrodactylus ascia n. sp., were recovered and described from the skin and gills of M. bleekeri. Species delimitation included the integration of morphometric analysis of sclerotised haptoral and reproductive structures with sequencing of the complete ITS rDNA region (ITS1-5.8S-ITS2) and partial 28S rDNA. Molecular comparisons showed substantial divergences from previously described species in two markers, ITS rDNA (19.12% in G. octoacanthicus n. sp.; 18.07% in G. ascia n. sp.) and 28S rDNA (16.83% in G. octoacanthicus n. sp.; 8.79% in G. ascia n. sp.), exceeding standard species-delineation thresholds. The newly compiled checklist included 17 taxonomically valid Indian species (including the two new species), of which sequence data are available for only seven, and eight nominal or undescribed species that were considered unavailable names due to non-compliance with the International Code of Zoological Nomenclature. The replacement names Gyrodactylus pandeyi nom. nov. and Gyrodactylus fossilisii nom. nov. were proposed for the junior homonyms, Gyrodactylus mizellei Dubey, Gupta & Agrawal, 1990 and Gyrodactylus gussevi Dubey, Gupta & Agrawal, 1990, respectively. These findings highlighted significant gaps in Indian gyrodactylid diversity and taxonomy and underscored the need for further integrative studies on parasite diagnostics, aquaculture-health management, and freshwater biodiversity conservation in India.