Response by Plectropomus-Leopardus and Other Serranid Fishes to Pearsonellum-Corventum (Digenea, Sanguinicolidae), Including Melanomacrophage Centers in the Heart

Adults of the blood fluke Pearsonellum corventum in the heart of Plectropomus leopardus from the Great Barrier Reef evoked a detectable response, but the continual production of their eggs induced a more significant response, including an abundance of melanomacrophage centres (MMCS) and granuloma formation in the ventricle as well as in other visceral organs. MMCs have not been recognised previously as a component of the ventricular spongiosis layer in fishes, but they were a normal feature of the infected and perhaps all P. leopardus as well as certain other serranids. Moreover, at least P. leopardus and certain nonserranid fishes from the Gulf of Mexico contain an abundance of free macrophages among ventricular myocardial and endocardia1 tissues. Because of those MMCS and free macrophages in P. leopardus, as well as an apparently independent extensive response involving pigmented fibrotic encapsulation of foreign bodies in the body cavity in that and other serranids from the Gulf of Mexico and Red Sea, P. leopardus and probably several other serranids should provide especially valuable models to assess macrophages and nonspecific pigmented foreign body responses. Sections in the heart of two serranids from other geographic regions exhibited what appeared to be different sanguinicolid eggs, and those fishes responded differently to P. leopardus.