First report of Ktariella polyorchis (Monogenea: Calceostomatidae) infection in farmed meagre Argyrosomus regius (Actinopterygii: Sciaenidae), with a review of calceostomatid parasites of wild and cultured fish

The present investigation reports a monogenean outbreak in broodstock of meagre Argyrosomus regius (Asso, 1801) from a Croatian farm. The parasites were visible by naked eye and were found in large numbers in the oral cavity and over the body surface. Morphological and molecular analyses allowed to identify the parasites as Ktariella polyorchis Vala & Euzet, 1977 (Monogenea: Calceostomatidae), here reported for the first time in farmed A. regius. Calceostomatids are known to parasitize different fish species of the family Sciaenidae worldwide: particularly, K. polyorchis had been described infecting the gills of wild A. regius caught off Tunisia and Egypt. This work provides the first detailed description of the parasite surface by SEM analysis, and the first molecular data (complete ITS and partial 28 S rDNA sequences), useful in future taxonomical and phylogenetic studies. Furthermore, we provide a synthesis of previous records of calceostomatid parasites of wild and cultured fish, highlighting their role as potential emerging parasites in the farming of sciaenid fish worldwide.