Background: Sparidae is a fish family that belongs to the order Perciformes and is commonly known as sea breams and porgies. Many species are included in this family and divided into 71 genera that could be barcoded using mitochondrial DNA genes. These fish are vulnerable to different parasitic taxa that affect fish status. The present study is aimed to confirm the molecular status of Argyrops filamentosus fish via the mitochondrial cytochrome c oxidase (COI) gene and to study the pathological changes of gills infested by monogenean parasites. 
 
Methods: Thirty Argyrops filamentosus fish were collected from Jeddah (Saudi Arabia) and identified molecularly via the mtCOI gene. Also, gills were isolated and examined microscopically for presence of monogeneans. Histopathological impacts of monogeneans on fish gills were studied in comparison to the gills of non-infected fish.&nbsp; 
 
Result: The DNA of fish species was barcoded and showed highly stringent criteria with the previously Argyrops filamentosus sequence data. The obtained host DNA sequences were deposited in NCBI database under accession number OP975758.1. Examination of the investigated fish gills revealed the presence of three monogenean species Protolamellodiscus senilobatus Kritsky, Jim&eacute;nez-Ruiz and Sey, 2000, Acleotrema maculatus Morsy, El-Fayoumi and Fahmy (2014) and Haliotrema susanae Soo, 2019. Monogenean parasites penetrated deeply with their haptor to the gill lamella and caused damage and degeneration of epithelial cells leading to the formation of a cup-shaped depression. Therefore, the mtDNA gene has the ability for host identification and heavy monogeneans infections lead to severe damage to fish gills.&nbsp;

DNA Barcoding of Argyrops filamentosus (Perciformes: Sparidae) Based on Mitochondrial COI Gene and Histopathological Evaluation of Gills Infected by Monogeneans