An integrated morpho-molecular and epidemiological study on a Benedenia sp. (cf. akajin) infecting the redspot emperor (Lethrinus lentjan) in the Arabian gulf.

The Redspot Emperor, Lethrinus lentjan Lacepède, 1802, is a commercially vital species in the Arabian Gulf fisheries, yet its parasite fauna remains inadequately documented. This study provides the first comprehensive morpho-molecular and epidemiological characterization of a monogenean parasite infecting L. lentjan in this region. Seasonal sampling of 400 fish from Jubail and Dammam revealed a Benedenia sp. (cf. akajin) exclusively parasitizing the gills. Integrated morphological analysis showed greatest similarity to Benedenia akajin, but differences in microhabitat (gills vs. body surface) and larger body size were observed. Molecular phylogeny based on partial 28 S rDNA (GenBank PX711249) confirmed close affinity with B. akajin (99.2% sequence similarity) and revealed limited genetic differentiation (0.8% uncorrected p-distance), with moderate nodal support (ML bootstrap 52%). Epidemiological analysis identified clear seasonal and spatial patterns: infection prevalence and intensity peaked during summer (up to 96% in Jubail) and were consistently higher in Jubail than in Dammam. Furthermore, a positive trend was found between host size and parasite burden. This study identifies a previously uncharacterized Benedenia population, closely related to B. akajin, as a significant parasite of L. lentjan in the Arabian Gulf. Given the limitations of the current evidence (single molecular marker, moderate phylogenetic support, and morphological overlaps with congeners); the parasite is provisionally designated as Benedenia sp. (cf. akajin). The findings delineate key risk factors - summer temperatures, the Jubail area, and larger host size - providing a scientific foundation for targeted health surveillance and sustainable management of this fishery.