A survey of parasitic crustaceans on the gills of two freshwater fish species in Southern Iraq, specifically in the Al-Gharraf River (Thi Qar Province), was conducted from December 2022 to December 2023. The results led to the discovery of a new species: Ergasilus luteusi sp. nov., found on both the yellow barbell, Carasobarbus luteus (Heckel) (type host), and the Abu mullet, Planiliza abu (Heckel). This new species shares a guitar-shaped cephalothorax with 11 other species of Ergasilus; however, Ergasilus luteusi sp. nov. differs from all these species, except for E. iraquensis Amado, 2001, in the armature of legs 1-4. Ergasilus luteusi is very similar to E. iraquensis, but it can be distinguished by possessing three setae in the terminal segment of leg 5 (only two setae in E. iraquensis). The ratio of the second endopod segment to the first endopod segment of the antenna is 65% in E. luteusi, compared to 80% in E. iraquensis. Additionally, the length-to-width ratio of the caudal rami in the new species is 1.5:1, whereas it is 1.1:1 in E. iraquensis.