Two different batches of meagre Argyrosomus regius were stocked in the same floating cage located in north-eastern Sardinia (western Mediterranean Sea). After 4 mo, the fish started showing non-specific disease signs, such as lethargy, emaciation, gill anaemia and mortality. In total 65 specimens of meagre of both stocks were sampled for parasitological and microbiological analysis, and only 1 species of parasite, the microcotylid monogenean Sciaenacotyle panceri, was found on the gills of caged meagre. No protozoan or other metazoan parasites were found and no bacteria or viruses were isolated. After the outbreak, a total mortality rate of 5 to 10% was estimated for the older fish stock, while no noteworthy mortality was recorded in younger fish (<2%). This is the first account of S. panceri on the gills of cultured meagre as causative agent of disease and mortality. The effects of the presence of this parasite emphasise the need for disease control strategies of cultured meagre, and investigating the transfer of microcotylids from wild to caged fish.