Polyopisthocotylean monogenean parasites of fishes are highly host specific and have been used as an appropriate model to study the host-parasite co-evolution. In the present study, eight monogeneans of the order Mazocraeidea were characterized by nuclear 28S rDNA sequences and their phylogenetic relationship with other polyopisthocotylean species was investigated. Neighbour-joining, maximum parsimony, maximum likelihood and Bayesian Inference methods were used for phylogenetic reconstruction. The topology sustained by high bootstrap was: (((Hexabothriidae (Mazocraeidae (Discocotylidae (Diplozoidae (Diclidophoridae (Plectanocotylidae (Heteromicrocotylidae (Microcotylidae (Heteraxinidae), (Thoracocotylidae, Gotocotylidae (Gastrocoylidae (Allodiscocotylidae: Protomicrocotylidae))). In addition, we have also developed DNA barcodes (COI sequences) for six species and the barcodes clearly discriminated all the species. The polytomy within Protomicrocotylidae family is resolved in this study for the first time and it appears that within this family, Bilaterocotyloides species are basal compared to Neomicrocotyle and Lethacotyle species while the latter is the more derived.

The aim of this study was to phylogenetically analyze Fasciola gigantica (F. gigantica) from mainland India and to reveal the expansion history of F. gigantica in the Indian subcontinent. We analyzed 40 Fasciola flukes that were collected from Delhi, in the Indian mainland, and identified them as F. gigantica by using nucleotide analyses of the nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) genes. Based on the nucleotide sequence of mitochondrial NADH dehydrogenase subunit 1 (nad1) gene, the flukes had 18 haplotypes. The haplotypes were classified under haplogroup A, which is predominant in the F. gigantica of South Asia. The population genetics of haplogroup A revealed that Delhi population showed higher π value than eastern India population. These results suggest that F. gigantica of haplogroup A might have spread from the west to the east in India along with the artificial migration of the domestic Zebu cattle, Bos indicus.

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The aim of this study was to analyze the phylogenetic relationship between Explanatum explanatum populations in India and other countries of the Indian subcontinent. Seventy liver amphistomes collected from four localities in India were identified as E. explanatum based on the nucleotide sequences of ribosomal ITS2. The flukes were then analyzed phylogenetically based on the nucleotide sequence of the mitochondrial gene nad1 in comparison with flukes from Bangladesh and Nepal. In the resulting phylogenetic tree, the nad1 haplotypes from India were divided into four clades, and the flukes showing the haplotypes of clades A and C were predominant in India. The haplotypes of the clades A and C have also been detected in Bangladesh and Nepal, and therefore, it seems they occur commonly throughout the Indian subcontinent. The results of AMOVA suggested that gene flow was likely to occur between E. explanatum populations in these countries. These countries are geographically close and have been historically and culturally connected to each other, and therefore, the movements of host ruminants among these countries might have been involved in the migration of the flukes and their gene flow.

In India, Labeo rohita is widely cultured and consumed freshwater fish. Aeromonads are etiological agents of major bacterial fish diseases like furunculosis, haemorrhagic septicaemia, skin ulcers, fin/tail rot and dropsy, causing significant economic losses in carp culture. Aeromonas species are widely distributed in aquatic environment which is considered as important vehicle of Aeromonas infections to fish and humans. Some of the Aeromonas spp. causes gastroenteritis, septicaemia, peritonitis, meningitis and eye infections in humans. In the present study Aeromonas species were isolated from diseased freshwater fish Labeo rohita collected from two districts viz., West Godavari and SPSR Nellore of Andhra Pradesh, India. A Total of 12 Aeromonas spp. were isolated and identified by biochemical tests. A. veronii bv. veronii (35%) was dominant when compared to other Aeromonas spp. Further, Antimicrobial resistance and multiple Antimicrobial resistance (MAR) of all Aeromonas spp. were tested against 17 antibiotics being frequently used for human diseases. The Antimicrobial resistance of all the 12 Aeromonas spp. have shown significantly high (p<0.05) resistance (100%) to ampicillin, amoxyclave and oxytetracycline except A. cavernicola when compared to other antibiotics. The MAR index of Aeromonas spp. ranged from 0.18-0.76, which indicates origination of isolated Aeromonas spp. from high risk sources of contamination. A. hydrophila, A. veronii bv. sobria, A. veronii bv. veronii, A. schubertii and A. jandaei isolated in this study were found to be pathogenic to humans also. The results revealed the pathogenic potential of Aeromonas infections in freshwater fish culture and emerging threats to public health.