Morphologic and biochemical characterization of erythrophoromas in goldfish (Carassius auratus).

The properties of spontaneous cutaneous erythrophoromas that occurred in 17 adult goldfish (Carassius auratus) were described. This study was based on combined histology, cytochemistry, electron microscopy, and biochemical analysis. Tumors that varied from 0.4 to 2.7 cm in maximum diameter were located on various parts of the skin. As shown by light microscopy, tumors were composed of red- to orange-pigmented, dendritic, stellate, or spindle-shaped cells, which coalesced into an excrescence in the dermal layer. No metastasis was observed. Evidence of invasiveness in five examples and local recurrence in three examples indicated that some of these tumors were malignant. Electron microscopy revealed numerous round cytoplasmic organelles (pterinosomes), which measured 0.4--0.7 mu, and well-developed tubular, smooth endoplasmic reticulum in the tumor cells. Biochemical analysis showed that red pigmentation of tumor cells was imparted by pteridines and carotenoids, most of which were detectable in normal adult erythrophores. These data indicate that tumors were comprised of neoplastic erythrophores.