Ecological and Hygienic-Sanitary Implications Related to the Diseases of the Mugilidae from ONR Capo Peloro

The aim of this thesis is to identify the different mullet species present in the Ganzirri Lagoon located in Messina, in order to study the main parasitic diseases and to deepen the knowledge of a wide range of morphometric and morphological characteristics of otoliths. One of the most common problems in fish is parasitic diseases. The presence of organisms that parasitize in the living tissues of other organisms involves a chronic inflammatory reaction, which causes an immune reaction with the formation of granulomas, typical lesions of chronic inflammation with different histological characteristics. Mullets (Osteichthyes: Mugilidae) represent a widespread species, they are euryhaline fish species capable of living and adapting to any habitat and represent a suitable study model for the development of lesions in the host-parasite interface. In this study 150 mullets, of three different species C. labrosus (99/150), C. auratus /L. aurata (37/150) and O. labeo (14/150), were studied. Initially, dichotomous keys were used to identify the three species. Subsequently, a fresh parasitological examination of the gastrointestinal tract (GIT) was carried out in which, acanthocephalan parasites were found in two specimens of C. labrosus, together with some cysts probably attributable to digenean trematodes metacercariae. in two specimens of C. labrosus. About 44.66% of the tested specimens were positive for digenean trematodes (C. labrosus, 49.5 %; C. aurata, 27% and O. labeo, 50%). In addition, the present work focuses on identifying the stages of granuloma development from the initial to the final phase of infection, characterizing the immune cells and the non-inflammatory components of the granuloma in the different phases. All mullet specimens were sampled, and the different organs were examined by histological analysis. Granulomas associated with trematode metacercariae parasites were classified into five developmental stages: (1) Free parasite, (2) Encysted parasite, (3) Early-stage granuloma, (4) Intermediate stage granuloma and, (5) Late-stage granuloma. This staging represents an effort in the knowledge of parasite-related granulomatous inflammation in fish organs as well as an attempt to relate granuloma stages to specific periods of the life cycle of the parasites. Moreover, in this study, a wide range of intra- and interspecific morphometric and morphological features in the otoliths of the three mugilid species has been investigated. In this regard, differences in otoliths among individual species were analyzed and compared. Scanning electron microscopy and stereomicroscopy were used to evaluate morphometric characteristics, variability between pairs of otoliths, and the external crystal structure of the acoustic sulcus. The positive correlation between the ratio of sulcus acusticus surface to the entire sagitta and the increase in specimens’ size was related to an accentuated sulcal growth, which could depend on species ecology and its adaptation to studied area. Furthermore, in the case of C. labrosus, a different morphology has been highlighted from those reported in the literature in fish from the western Mediterranean and Atlantic Ocean, showing a remarkably higher rectangularity, while the circularity was by far lower. C. labrosus was the only one species to show a slight difference between the left and the right sagitta, particularly with reference to the acoustic sulcus. These small changes between left and right sagitta are most probably due to ecology and feeding strategies. Morphological differences between specimens from different geographical areas could lead to changes in sagitta among stocks and could depend on the environmental characteristics of Ganzirri lagoon. This study may expand the knowledge of sagitta morphological functionality, fish adaptation to different environmental factors, and give a better understanding of tissue reaction associated with trematodes metacercariae.