Studies on the morphological and histological aspects of color abnormalities in flatfishes

本研究从形态学和组织学的角度对比目鱼种鱼生产中出现的颜色异常，特别是白化现象进行了分析，并探讨了其发生机制。用两种不同的活饵料饲养两组牙鲆幼鱼，其中一组幼鱼在变态完成时呈现正常的色素沉着，另一组幼鱼则呈现几乎完全的白化。两组仔稚鱼各发育阶段的形态测量结果无显著差异。在此基础上，对日本鳎异尾轮虫白化幼鱼和正常色素幼鱼进行了比较研究。白化组幼鱼眼侧头部呈现盲侧的形态特征，变态完成后，正常组幼鱼仅眼侧出现快速色素沉着。在同一时相，白化组眼侧无事件发生，白化区与盲侧色素细胞分布相同。电镜和光镜观察表明，白化病组眼肌侧出现了本应在盲侧观察到的色素母细胞分化。粘液细胞的分布表明，在变态初期，皮肤的不对称分化就开始了，而白化组仔鱼的这种不对称分化则受到抑制，这表明扁平鱼类眼侧的色素沉着与变态期皮肤的分化密切相关。比目鱼的赤眼病来源于仔鱼皮肤的“盲侧分化”。

The subjects of this study were to analyze the color abnormalities, especially albinism which occur in seed production of flatfishes from a view point of morphology and histology, and to discuss about the mechanism of this abnormality. Two groups of larval flounder Paralichthys olivaceus were raised with two different live foods, juveniles from one of them showed normal pigmentation and those from another showed nearly complete albinism at the completion of metamorphosis. Morphometric measurement of larvae and juveniles from these two groups at each developmental stage showed no significant difference. Then albinic juveniles of Japanese sole Heteromicteris japonicus were compared with normally pigmented juveniles which were raised from eggs in the laboratory. Albinistic head area of the ocular side showed the morphological characteristics of the blind side.At the completion of metamorphosis, normal group juveniles shows quick pigmentation on the ocular side only. At the same phase, no event occurred on the ocular side of albinic group, and the albinic area showed the same distribution of pigment cells on the blind side. Electron and light microscopic observation on larval skins from the above-mentioned two groups showed that the differentiation of the chromatoblast which should be observed on the blind side occurred the ocular side of albinic group. The distribution of mucus cells which were typical cells on the normally pigmented ocular side showed asymmetrical differentiation of skin occurred from the onset stage of metamorphosis, and this asymmetrical skin differentiation was inhibited in the albinic group larvae.These results suggested that pigmentation on the ocular side of flat fishes was closely related with the differentiation of skin through metamorphosis, and alninism of flat fish was derived from "the blind side differentiation" of larval skin.