<p>A spontaneous skin tumour in an adult wild female deep-bodied mojarra, <i>Gerres erythrourus</i> has been recorded. Gross examination revealed a white, fleshy tumor growth located on the anterior and right side of the fish. The mass was attached to the flank between the pectoral and pelvic fins, where a distended, tumor-like structure was evident. The tumour was invasive and extended beyond the deep margins of the biopsy specimen. Necropsy examination showed no evidence of tumour spread to other visceral organs. Histopathologically, the tumours growth was characterized by monomorphic spindle cells, which has small, oval and hyperchromatic nuclei. The cytoplasmic border of spindle cells was unclear and contained moderate to abundant of fine to coarse light refractile golden-brown to olive-green pigment granules. On the basis of the clinical and histolopathological findings, this tumour was diagnosed as iridophoroma. TEM analysis of the tumours from <i>G. erythrourus</i> clearly showed tumour associated virus-like particles which might be the cause of tumours.</p>