Generation of a white-albino phenotype from cobalt blue and yellow-albino rainbow trout (Oncorhynchus mykiss): Inheritance pattern and chromatophores analysis

Albinism is the most common color variation described in fish and is characterized by a white or yellow phenotype according to the species. In rainbow trout Oncorhynchus mykiss, aside from yellow-albino phenotypes, cobalt blue variants with autosomal, recessive inheritance have also been reported. In this study, we investigated the inheritance pattern and chromatophores distribution/abundance of cobalt blue trouts obtained from a local fish farm. Based on crosses with wild-type and dominant yellow-albino lines, we could infer that cobalt blue are dominant over wild-type and co-dominant in relation to yellow-albino phenotype, resulting in a fourth phenotype: the white-albino. Analysis of chromatophores revealed that cobalt blue trouts present melanophores, as the wild-type, and a reduced number of xanthophores. As regards to the white-albino phenotype, they were not only devoid of melanophores but also presented a reduced number of xanthophores. Cobalt blue and white-albino trouts also presented reduced body weight and a smaller pituitary gland compared to wild-type and yellow-albino phenotypes. The transcription levels of tshb and trh were up regulated in cobalt blue compared to wild type, suggesting the involvement of thyroid hormone in the expression of blue color. These phenotypes represent useful models for research on body pigmentation in salmonids and on the mechanisms behind endocrine control of color patterning.白化症是鱼类中最常见的体色变异类型，根据物种不同，其表现为白色或黄色表型。在虹鳟（Oncorhynchus mykiss）中，除黄色白化表型外，还曾报道过呈常染色体隐性遗传的钴蓝色变异体。本研究针对从当地渔场获取的钴蓝色虹鳟，对其遗传模式以及色素细胞的分布与丰度展开了探究。通过与野生型及显性黄色白化品系的杂交实验，本研究推断：钴蓝色表型对野生型呈显性，而与黄色白化表型则呈共显性，由此产生了第四种表型——白色白化型。色素细胞分析结果显示，钴蓝色虹鳟与野生型个体同样含有黑色素细胞，但其黄色素细胞数量有所减少。对于白色白化型个体而言，它们不仅完全缺失黑色素细胞，黄色素细胞数量也同样出现了减少。与野生型及黄色白化型个体相比，钴蓝色和白色白化型虹鳟的体重更低，垂体体积也更小。相较于野生型个体，钴蓝色虹鳟体内tshb与trh的转录水平均出现上调，这提示甲状腺激素参与了蓝色体色的形成机制。上述表型可为鲑科鱼类的体色调控研究以及体色模式的内分泌调控机制研究提供极具价值的实验模型。