Histological and Lectinhistochemical Pattern of the Inflammatory Response to Ascocotyle sp. Metacercariae in Mugil liza Hearts

Abstract

Simple Summary Fish, like all animals, defend themselves against injury and infection by sending immune cells to the affected organ. Some parasites spend part of their life cycle inside fish, where they form cysts in various organs, including the heart. In the mullet’s heart, these cysts are usually reported in the bulbus arteriosus, and only rarely in its main muscular chamber, the ventricle. We found such cysts in the ventricle of the lebranche mullet, a species of commercial value in South America, and examined how the fish responded to them, using several staining methods, including one based on proteins that bind to specific sugar molecules on cells. We identified four types of immune cells around the cysts and successfully distinguished two of them for the first time in this species. We also found that prolonged inflammation damaged the surrounding heart muscle, an effect not previously described in this fish. These results clarify how mullets react to parasites and provide a reference point for assessing the health of wild and farmed populations.