Department of Life Science, Faculty of Science and Technology, Kindai University, Higashiosaka, Japan.
J Fish Biol. 2020 Apr;96(4):1014-1023. doi: 10.1111/jfb.14293. Epub 2020 Feb 27.
Boldness and risk-taking behaviours in animals are important traits to obtain advantages such as habitation, food resources, reproductive success and social dominance. Risk-taking behaviour is influenced by physiological and environmental conditions; however, whether individual fish become bolder by the presence of conspecifics remains unknown. In this study, a light-dark preference test was conducted using medaka fish (Oryzias latipes) with or without a neighbouring conspecific. It was found that individual medaka male fish preferred a light environment and avoided a dark environment, whereas the display of a neighbouring conspecific enhanced the time the male spent in the dark environment (i.e., this condition encouraged risk-taking). The blood glucose level increased in fish confined to the dark condition but did not increase in light-preferring fish and risk-taking fish. Large somata expressing tyrosine hydroxylase, which is the rate-limiting enzyme in dopamine synthesis, were detected in the telencephalic and diencephalic brain regions in risk-taking medaka, whereas large somata were detected in the diencephalic region in medaka confined to the dark condition. These findings indicated that medaka is a good fish model to explore the central roles of dopaminergic neurons in the telencephalon and the diencephalon, which regulate risk-taking behaviour.
动物的大胆和冒险行为是获得优势的重要特征，例如栖息地、食物资源、繁殖成功和社会统治地位。冒险行为受生理和环境条件的影响；然而，个体鱼类是否会因为同类的存在而变得更加大胆，目前尚不清楚。在这项研究中，使用斑马鱼（Oryzias latipes）进行了明暗偏好测试，其中包括有或没有邻近同种鱼的情况。结果发现，雄性斑马鱼更喜欢明亮的环境，避免黑暗的环境，而邻近同种鱼的存在会增加雄性在黑暗环境中的停留时间（即，这种情况鼓励冒险）。被限制在黑暗环境中的鱼类的血糖水平会升高，但喜欢明亮环境和冒险的鱼类的血糖水平不会升高。在冒险的斑马鱼的端脑和间脑的脑区中检测到表达酪氨酸羟化酶的大神经元，酪氨酸羟化酶是多巴胺合成的限速酶，而在被限制在黑暗环境中的斑马鱼的间脑区中检测到大神经元。这些发现表明，斑马鱼是一种很好的鱼类模型，可以探索调节冒险行为的端脑和间脑多巴胺能神经元的中枢作用。
