Liver lesions in cultured Oreochromis hybrids caused by amoeboid organisms similar to the aetiological agent of goldfish kidney granuloma

Abstract

Autopsies of cultured hybrid cichlids (Oreochromis aurea × nilotica) from dying-off overwintering stock revealed focal white lesions in the liver, which, upon histological examination, were found to be filled with masses of amoeboid organisms. These were reminiscent of the causative agents of goldfish kidney granuloma. The lesions were granulomata comprised of degenerating epitheloid cells surrounding a gradually expanding necrotic core. The amoeboid organisms occurred both inside and outside the host cells, and in the granuloma's cellular and necrotic components; a few were also found in the surrounding liver cells.