In fishes, neoplasia is generally a benign condition. However, few malignant diseases have been
reported previously. Fibromas are benign and non-functional tumors composed of bundles of
spindle-shaped cells having fibroblastic appearance arranged in a whorling or storiform pattern
along with abundant collagen. A surgically removed mass from second dorsal fin of white skirt tetra
(Gymnocorymbus ternetzi) with the history of unbalance swimming was referred to the Diagnostic
Pathology Laboratory, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran. Light
microscopy revealed the presence of abundant collagen fibers in repetitive interwoven patterns
along with spindle-shaped fibrocytes arranged in a whorling pattern presenting the histopathological
feature of fibroma. Since carcinogenic compounds, viruses, irritants and parasites can be involved
in fish benign tumors development, predisposing factors should be monitored carefully to promote
animal welfare.
