Abstract
A giant grouper, Epinephelus itajara (Lichtenstein), was found dead in its tank. The principal necropsy findings consisted of multiple tumors in the ventricle of the heart, a tumor mass in the stomach, and protozoa-like organisms in the heart tumor, bile ducts and kidney collecting ducts. The heart tumors were identified as mesotheliomas and the stomach tumor as a papilloma. The morphology of the protozoan-like organisms was similar to that of Rhabdospora thelohani (Languesse).