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Prevalence, molecular identification and host preference of Dactylogyrus, an ectoparasite in Indian major carps

Aim: The present study was carried out to ascertain the prevalence and species-spectrum of Dactylogyrus in Indian major carp farms of Odisha state, India. Further it is to establish host preference of Dactylogyrus catlaius among Indian major carps.. Methodology: The study was conducted from September 2018 to March 2020 in thirteen districts of Odisha. During that period, total 786 fish samples comprising of Labeo rohita, Catla catla and Cirrhinus mrigala were examined using Level II diagnosis. A total of 25 Dactylogyrus positive samples identified using microscopy representing all the districts have been amplified using 28S rDNA PCR and sequencing. Secondary structures for 28S rDNA fragments were predicted using MFold package (version 3.5) software. To ascertain host preference of D. catlaius a standard co-habitational challenge method was followed in which infected fishes were kept together with healthy fishes (all three Indian major carps). Results: Total 786 fish samples comprising of Labeo rohita, Catla catla and Cirrhinus mrigala, all three Indian major carps were examined and overall prevalence of 64.50% for Dactylogyrus spp. was found. Further, winter season was the most favoured season whereas L. rohita was the most preferred host for this parasite. A total of 25 Dactylogyrus isolates, i.e., 22 Dactylogyrus catlaius, two D. vastator and one D. scorpius were identified using 28S rDNA PCR and sequencing. Hence, D. catlaius has been identified as the most prevalent Dactylogyrus species in Odisha. Secondary structures for 28S rDNA fragments of three Dactylogyrus spp. were also predicted reflecting their diversity. Further in a cohabitational challenge study, D. catlaius was found to be a generalist parasite infecting all three Indian major carps with a higher preference for rohu L. rohita. Interpretation: The present study provides a holistic information regarding Dactylogyrus prevalence in the state of Odisha. Further, the study illustrates host-parasite relation of D. catlaius among Indian major carps which would strengthen knowledge on developing any prophylactic measure in future.