Morphological Variability and Molecular Studies of Argulus japonicus from Cyprinus carpio in Sulaymaniyah Province

Abstract

Background and Objective: Argulus japonicus is an important ectoparasitic crustacean that causes significant health and economic problems in freshwater aquaculture. This study aimed to determine the prevalence and provide morphological, ultrastructural, and molecular characterization of A. japonicus infecting common carp (Cyprinus carpio) in the Kurdistan Region of Iraq.

Material and methods: A total of 174 fish samples were collected between June 2021 and May 2022. The skin, fins, and gills were examined for A. japonicus infestation. Parasites were identified using light microscopy and scanning electron microscopy (SEM). Genomic DNA was extracted, and the nuclear 28S rDNA gene was amplified by polymerase chain reaction (PCR) and sequenced. The obtained sequences were compared with those available in GenBank, and phylogenetic analysis was performed.

Results: A. japonicus was detected with an overall prevalence of 8.62%. Morphological and ultrastructural analyses differentiated the adult male and female parasites and identified the metanauplius larval stage. The presence of claspers at the base of the swimming appendages and branched dorsal ridges represented key diagnostic characteristics for the identification of A. japonicus. Molecular analysis of the 28S rDNA gene showed 99–100% sequence identity with reference sequences available in GenBank, confirming species identity. The obtained sequences were deposited in GenBank, and phylogenetic analysis demonstrated close genetic relationships with previously reported A. japonicus isolates.

Conclusion: This study provides the first comprehensive morphological, ultrastructural, and molecular characterization of A. japonicus infecting C. carpio in Iraq. It also represents the first record of A. japonicus in common carp from the Kurdistan Region, expanding the known geographical distribution of this economically important parasite and providing valuable baseline data for future taxonomic and epidemiological studies.