The fish host (Wallago attu) and monogenoid parasite (Thaparocleidus sp.) have been recorded during 2 years (2011 and 2012) to investigate intra/interspecific interactions among query species (T. sudhakari (Gusev, 1976) Lim, 1996; T. indicus (Kulkarni, 1969) Lim, 1996; T. gomtius (Jain, 1952) Lim, 1996; T. yogendraii Agrawal, 1981 and T. wallagonius Jain, 1952) in the light of parasitic worm burden, morphological and molecular data. Each species is highly host specific (oioxenous), with a specialized functional niche. Being niche specialists, they exhibit niche overlapping along with co-existence due to reproductive barrier. Furthermore, a molecular marker, affirming clear-cut genetic variation in spite of structural entities, provides evidence for infra-speciation as well as co-speciation.

23 SummaryThaparocleidus 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.

Sperata aor commonly called as long- whiskered cat fish or “Bada Tengan” in local fish markets harboured one new and one previously known species of genus Thaparocleidus Jain, 1952, along with two species of Cornudiscoides Kulkarni, 1969, infesting gills. Thaparocleidus aori (Rizvi, 1971) Lim, 1996, was earlier described by Rizvi therefore was briefly recorded in the present study, except the egg. The newly found species Thaparocleidus susanae n.sp was characterized by the structure of its peculiar copulatory organ. Phylogenetic relationship of the two species under study, along with 14, reterived from GenBank was established using the sequences of 28S rDNA region (Dactylogyrus Diesing, 1850 taken as an out group).

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Thaparocleidus devraji [8,12] from Ompok malabaricus [27] was established by Gusev [8]. However, its description was based only on the hard parts. On a careful examination of its live specimens from an additional host and a new locality i.e. river Gomti of Lucknow, structural details of the parasite were added, including its egg. Furthermore, phylogenetic relationship was also established with other Indian species of this genus using Urocleidus similis and Ancyrocephalus paradoxus included in an out group. Sequence analysis of partial 28S rDNA had been done using Minimum evolution (ME), Neighbour-joining (NJ) and UPGMA method of MEGA 5 (Molecular Evolutionary Genetics Analysis-5, Tamura et al. [20]). Furthermore, secondary RNA structure, centroid structure, ss-count, energy dot plot and motif identification had been done, along with GC calculation (for conservedness). All the species of this genus under study, had been found morphologically distinct (reproductive and haptoral armature). The morphological distinctions had been supported by genetical evidences. The results of phylogeny had shown that all the species (understudy) are genetically distinct and T.devraji had monophyletic origin.