Histopathological and immunohistochemical characterization of host-parasite interaction in visceral organs of mullets (Osteichthyes: Mugilidae) from Sardinian lagoons

Parasitic diseases in fish constitute a limiting factor for wild fishes and for aquaculture production. Extensive aquaculture in Sardinia is an important economical and traditional issue and mullets represent the most important product of this farming system.The aim of this study was to evaluate host-parasite interaction in visceral organs of Mugilidae species from Sardinian lagoons. A total of 239 mullets of different species were collected from four Sardinian lagoons. Lesions were examined macroscopically and histologically and also using histochemical and immunohistochemical techniques. Prevalence of Metazoan parasites (Digenean metacercariae, Myxobolus spp.andPolysporoplasma mugilis) were evaluated.MetacercariaeandMyxobolus sppinfections showed a similar prevalence in all lagoons, whereas a high prevalence of P.mugilis was observed in Cabras lagoon. Kidney was the most affected organ both for Metacercarie e Myxobolus species. Cellular immune response displayed a particularly relevant role with the development of chronic granulomatous reaction against parasites. Macrophages, epithelioid cells and fibroblasts were identified by immunohistochemestry as the main constitutive cell populations of granulomas but also eosinophilic granular cells and rodlet cells were associated to this response. Study of the granuloma structures revealed that Mugilidae displayed a common response against different metazoan parasites in visceral organs.