Molecular characterization of Lamproglena monodi infesting Oreochromis niloticus in Egypt based on 18S and 28S rDNA markers.

This study investigated the molecular, morphological, and pathological characteristics of the parasitic copepod Lamproglena monodi infesting Oreochromis niloticus in Egyptian aquaculture. A total of 273 tilapia were examined from three governorates, with infestation frequencies of 25% in Kafr El-Sheikh, 20% in Giza, and 21.7% in Al-Sharqia. Seasonal frequencies ranged from 13% in summer to 34.3% in autumn. Molecular amplification produced fragments of 1405 bp (18S rDNA) and 737 bp (28S rDNA), and BLAST analysis confirmed their identity as L. monodi with ≥98% similarity to reference sequences. Phylogenetic reconstruction placed the isolates within the established Lamproglena clade. Histopathological examination of infected gills revealed lamellar destruction, telangiectasia, epithelial hyperplasia, and vascular congestion, consistent with the observed respiratory distress in affected fish. These findings provide the first integrated molecular and pathological confirmation of L. monodi in Egyptian tilapia and highlight its potential to impair gill function and reduce productivity under intensive aquaculture conditions. Enhanced surveillance and targeted parasite management strategies are recommended to mitigate the impact of this ectoparasite on tilapia health and farm sustainability.