Monogenoidea on exotic Indian freshwater fishes. 2. Range expansion of Thaparocleidus caecus and T. siamensis (Dactylogyridae) by introduction of striped catfish Pangasianodon hypophthalmus (Pangasiidae)

Thaparocleidus caecus and Thaparocleidus siamensis are parasitic monogeneans found on the gills of striped catfish Pangasianodon hypophthalmus (Pangasiidae), a native species of Southeast Asia. We report T. caecus and T. siamensis, for the first time in India, from the gills of aquarium-kept P. hypophthalmus (prevalence 40 % and 80 % respectively). We also report T. siamensis from the gills of pond-cultured P. hypophthalmus (prevalence 100 %); no specimen of T. caecus was observed on pondcultured P. hypophthalmus (prevalence 0 %). Morphometric data of the studied parasites did not differ significantly from previous descriptions of the two species recovered in other geographic locations. Similarly, no consequential variation was found when 28S rDNA of T. siamensis from the present study was compared with that of T. siamensis from Malaysia available on GenBank. The present investigation adds to growing cases of freshwater monogeneans that have been concomitantly introduced worldwide as a result of aquarium and aquaculture trade.