Histological, histochemical and morphometric changes of splenic melanomacrophage centers (Smmcs) in sparicotyle-infected cultured sea breams (Sparus aurata)

Diseases caused by parasites are much more frequently described in cultured fish, which suffer from artificial conditions and numerous stress factors. This study investigates the histological, histochemical and morphometric modifications of splenic melanomacrophage centers (SMMCs) infected by Sparicotyle chrisophrii (Monogenea, ectoparasite of the gills) in sea breams (Sparus aurata), cultured in floating cages in the Gulf of Gaeta (Italy). Infected fish swam near the water surface, showing severe signs of anemia. Several spleens were collected from both healthy and dead fish (70-100 gr. body weight). A spleen histopathology was evaluated by using traditional stainings, such as Haematoxylin and Eosin (HE), Periodic Acid-Schiff reaction (PAS), Perl's reaction for haemosiderin and Schmorl's reaction for lipofuscins. Furthermore, SMMCs morphometry was performed on PAS-stained sections to study 7 morphometric parameters [Mean SMMCs profile area (MPA), Mean SMMCs maximum diameter (Media), Mean SMMCs minimum diameter (media), Mean SMMCs diameter (Dia), Mean SMMCs Perimeter (P), Mean SMMCs Form Factor (FF) and Mean SMMCs number per square millimeter of spleen tissue (MN)]. A light microscope of HE stained sections of spleen revealed a dramatic increase in the size and number of SMMCs in parasitized animals. Morphometric data illustrated statistically significant differences (p < 0.01) of all studied parameters between healthy and diseased fish. This study emphasizes the importance of using histopathological investigations to unravel the complex biological host/parasite interaction, which results in systemic lesions affecting reared marine species.