Linking Caligus pageti Infestation to Grey Mullet Mortality in a Mediterranean Lagoon: First Molecular Characterization

Between November 2024 and February 2025, mass mortality events affecting grey mullets (Liza ramada and Mugil cephalus) were recorded in the Albufera des Grau, Menorca, resulting in approximately 5000 dead individuals. Gross examination revealed high levels of parasitic infestation and lesions, located on the skin and gills, typical of copepod infection. In addition, histological and molecular analyses were performed on selected potential pathogens to assess their possible contribution to fish mortality. This study focused on the molecular characterization of the ectoparasitic copepod Caligus pageti, providing the first genetic reference for the species. This enabled preliminary taxonomic and biological assessment despite the absence of previously available sequence data. Environmental measurements across the lagoon indicated conditions capable of sustaining the development, survival and proliferation of the copepod population. These findings highlight the importance of integrating morphological and molecular analyses to enhance understanding of the biology of C. pageti, providing a key reference for future studies on parasitic copepods in lagoon ecosystems.