Prevalence, morphological, and molecular redescription with ecological correlation of Livoneca redmanii (Isopoda, Cymothoidae) infection in Egyptian sole, Solea aegyptiaca

Abstract Isopod taxonomy and ecological correlation are the primary challenges constraining control strategies for fish. 600 Egyptian sole ( Solea aegyptiaca ) and water samples were collected regularly across the three sectors of Qarun Lake in 2024. An in-depth morphological description of the collected free-swimming and attached isopods identified Livoneca redmanii Leach, 1818. Identification was confirmed by the close evolutionary relationship of L . redmanii isolates among the three sectors, as evidenced by sequencing and phylogenetic analysis of COI and 16S rRNA genes. Sequence data from both genes were deposited in GenBank, each with a unique assigned accession number. The utility of COI as a robust barcode for Cymothoidae, in contrast to the more conserved 16S rRNA, was further supported, aligning with best practices for species-level resolution. Isopod-infested fish exhibited respiratory distress, skin erosion, hemorrhagic patches, branchial damage, morbidity, and mortality. The highest prevalence rate of isopod was recorded in the west sector (82.5%), with the summer showing the highest prevalence across all three sectors. The west sector also exhibited the highest mean infestation intensity of 3.6 isopods per fish, compared to 1.8 and 2.6 isopods per fish in the middle and east sectors, respectively. A higher fish condition factor of 1.01 was reported in the middle sector, while lower values of 0.85 and 0.61 were observed in the east and west sectors, respectively. Physicochemical water analysis revealed elevated pH, total ammonia, salinity, turbidity, and lower dissolved oxygen, particularly in the west sector during the summer. The current study provided a detailed morpho-molecular description of L . redmanii in the Egyptian sole, along with spatial and temporal prevalence correlated to ecological factors. These findings emphasize the importance of implementing efficient control protocols that target these destructive invasive isopods.