Research Product

Formation of hepatic melano-macrophage centres (MMC's) in Rivulus marmoratus was induced with the coccidian parasite Calyptospora funduli. Experimental infections were produced by feeding infected intestine and hepatopancreas from grass shrimp (Palaemonetes pugio) to individual parasite-free fish. Livers of fish samples 5-150 d post-infection were examined histologically. Mild diffuse inflammation, initiated during early merogony (5-8 d), consisted of eosinophilic granulocytes and heterophils. Liberation of merozoites (8-12 d) resulted in extensive hepatocyte degeneration which augmented leukocyte exudation considerably. During gamogony (15-18 d), mononuclear cells became a predominant component of the cellular exudate. Focal lesions considered to be early MMC's became apparent during early sporogony (20-25 d). Pigment content increased progressively; melanin, however, was never a major component. Oocysts first elicited a granulomatous reponse between 40 and 50 d. This suggests that MMC formation in this case is an inflammatory process in which mononuclear cells recruited from peripheral circulation play a dominant role. MMC development appears to be elicited by macrogamont degeneration, whereas granuloma formation probably is a response to oocysts.