Marine water fish is considered as important model to investigate the community and evolutionary ecology of parasites. Identification of parasites is not an easy task because they are usually very small, soft bodied and possess little morphological characters. In this regard, sharks carry various helminth parasites and among them, cestode specie is abundant.
Paraorygmatobothrium floraformis is a cestode and belongs to order Tetraphyllidea. These parasites are thin, small and milky white in color measuring 12-17 cm in length, acraspedote and apolytic. This parasite was isolated from the spiral intestine of commercially available elasmobranch fish, Rhizopriondon acutus in Bengal.
Considerable progress can be observed in case of phylogenetic research of tapeworms (Eucestoda) and rDNA clusters are proved to be effectual means for genetic studies1. In some investigations, scientists used nuclear large subunits 28S ribosomal DNA of cestode Paraorygmatobothrium floraformis and selected the segment of 28S rDNA gene to determine interspecific phylogenetic relationships with other cestode groups2. Same ribosomal DNA part was used by other scientists also to resolve the taxonomic issues of helminth parasites3. This particular region is useful because it generates repeated copies which provide a huge number of target sequences for PCR amplification4. Moreover, it is convinient to amplify even small quantities of DNA and these markers are also widely utilized for taxonomic studies5.
Acordingly, Chadamala Srinivasa Kalyan and Anu Prasanna Vankara6 conducted a research to assess the morphological criteria, molecular characterization of Paraorygmatobothrium floraformis by means of the 28S ribosomal DNA and to examine the phylogenetic position of this species with bioinformatics tools like BLAST and Mega 6. For this purpose, scientists obtained the milk shark, Rhizopriondon acutus from the local fisherman and the nearby Coastal areas of Nellore to analyze the cestodes from their spiral intestines. They were preserved in FAA (Formalin-10 mL, Alcohol-85 mL and Acetic acid-5 mL) for further morphological analysis. Furthermore, some parasites were fixed in 95% molecular grade ethanol and placed at low temperature of -20̊C for further molecular examination.
It was found that Elasmobranchs play a key role in commercial fisheries in many countries of the world including India. Most of these fishes are favorable to be consumed as a human food but the presence of cestode in their spiral intestine is very heavy. Moreover, identification of this parasite is not easy by means of morphological analyses. Therefore, research team used Ribosomal DNA to resolve the taxonomic issues in helminth identification. Conclusively, this type of studies can discover the link between different orders, families and species of the cestode parasites from the marine environment.
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17 November, 2019