QUANTIFICATION OF HISTOPATHOLOGICAL CARDIOTOXICITY IN Cyprinus carpio EXPERIMENTALLY INFECTED WITH Provednecia spp.

Bacterial infections pose a significant challenge to global aquaculture. The role of the Gram-negative bacteria, Providencia, in fish cardiotoxicity is a growing concern. This study aimed to investigate the histopathological heart damage in the common carp (Cyprinus carpio) after experimental infection with Providencia alcalifaciens. Carp were inoculated intraperitoneally with a P. alcalifaciens suspension and observed after seven days. A semi-quantitative histoscore system was employed to quantify the lesions, assigning importance factors and score values to pathological alterations. Gross examination showed the presence of white patches on the infected hearts. Microscopically, a variety of alterations were observed, ranging from mild to severe histopathological lesions. The most significant and prevalent lesions were severe hypercellularity (infiltration of inflammatory cells) in the epicardium (32%) and myocardium (22.67%). Other main findings involved hyperemia and oedema (13.33% each), and severe degenerative changes such as Zenker necrosis and Nuclear displacement (9.33% each). This investigation established a prominent order of severity with hypercellularity as the dominant change, as well as circulatory disturbances (hyperemia and oedema), and necrosis/nuclear displacement. The findings suggested that P. alcalifaciens experimentally induces significant and measurable cardiotoxicity in C. carpio, and the histopathological assessment provides a robust method for evaluating the severity of bacterial heart disease in farmed fish.