Chromatophoroma in a crevice kelpfish (Gibbonsia montereyensis)

A captive adult crevice kelpfish, Gibbonsia montereyensis, developed a cutaneous mass, approximately 9 × 7 mm on the right side of the head in an area of nonscaled skin. Following surgical debulking, examination of both impression smears and histologic sections of the tumor revealed a predominant population of round to spindloid to polygonal cells with a moderate amount of lightly basophilic cytoplasm. The cytoplasm was filled with round, variably-sized reddish-brown granules that often obscured the nucleus. Nuclei were round to ovoid with coarsely granular chromatin. There was minimal anisocytosis and anisokaryosis. The cytoplasmic granules in histologic sections were weakly positive by the Fontana-Masson method, and staining was eliminated with melanin bleach. Immunohistochemical staining was strongly positive with a murine monoclonal antibody for melan A. As the specificity of melan A for melanophores is not clearly defined in nonmammalian species, the tumor was examined by transmission electron microscopy. Melanophores were not detected. Instead, neoplastic cells were filled with numerous intracytoplasmic organelles with triple-limiting membranes composed of concentric lamellae; these structures were most compatible with pterinosomes, which are the pigment-containing organelles of cells called xanthophores and erythrophores. As both of these organelles are ultrastructurally indistinguishable and as kelpfish skin is known to contain both xanthophores and erythrophores, a diagnosis of a mixed pigment cell tumor or chromatophoroma was made. As the tumor was grossly reddish-brown, the possibility of a neoplastic population of only erythrophores could not be excluded. Pigment cell tumors, arising from cells of the embryonic neural crest, are common in reptiles and bony fish.     

圆斑星鲽仔稚鱼色素细胞发育和体色变化

为研究圆斑星鲽早期发育过程中色素细胞的形态和分布,实验对1~72日龄的圆斑星鲽鱼苗进行了连续的显微观察,并绘制了早期发育生长曲线。结果显示,圆斑星鲽从20日龄开始进入快速的增长期,在水温12~19.5°C时完成变态发育需要50 d,黑色素细胞最早出现,数量最多,黄色素细胞次之,虹彩细胞最后发育,数量最少。变态前黑色素细胞密度先升高后降低,在9日龄密度最大为1390个/mm~2,色素细胞逐渐密集鱼体两侧对称分布;变态开始后鱼体两侧色素不对称,有眼侧体表黑色素细胞逐渐溶解消退,由成体黑色素细胞代替,体色变深,黑色素细胞密度稳定在150个/mm~2;无眼侧黑色素细胞逐渐消溶退化,体色逐渐变白。白化个体在变态开始后出现,有眼侧不能形成成体黑色素细胞,形成白化。