Fish that display schooling and social behaviors are expected to show stress responses when they are challenged by isolation. Medaka exhibit social behavior in group situations, but little is known about the effects of social isolation on their physiological stress responses. Here, we subjected male medaka to several different housing situations and assessed whether the stress responses differed between grouped and isolated fish. Social isolation decreased plasma cortisol and increased brain serotonin [5-hydroxytryptamine (5-HT)] levels in male medaka irrespective of whether or not the isolated fish could visually perceive another individual. However, heat shock treatment, a grouped situation, and a paired situation increased plasma cortisol and decreased brain 5-HT levels. These results suggest that, in male medaka, physical contact among individuals is more stressful than isolation. Moreover, both grouped and paired fish had lower tryptophan hydroxylase 2 (Tph2) expression levels than isolated fish, whereas heat shock downregulated both Tph1 and Tph2. The present study indicates that, in fish, the magnitude of reduction in brain Tph1 and Tph2 expression levels and serotonin concentration varies with the type of stress.

中文翻译：

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雄性鳉鱼对社会隔离的生理变化

表现出学校教育和社会行为的鱼类在受到孤立挑战时会表现出压力反应。Medaka 在群体环境中表现出社交行为，但人们对社交孤立对其生理压力反应的影响知之甚少。在这里，我们将雄性青鳉置于几种不同的居住环境中，并评估分组鱼和孤立鱼的应激反应是否不同。社会隔离会降低雄性青鳉的血浆皮质醇水平并增加脑血清素 [5-羟色胺 (5-HT)] 水平，而不管被隔离的鱼是否能在视觉上感知另一个人。然而，热休克治疗、分组情况和配对情况会增加血浆皮质醇并降低大脑 5-HT 水平。这些结果表明，在雄性青鳉中，个人之间的身体接触比孤立更有压力。此外，成组鱼和成对鱼的色氨酸羟化酶 2 (Tph2) 表达水平低于孤立鱼，而热​​休克下调了 Tph1 和 Tph2。本研究表明，在鱼类中，脑 Tph1 和 Tph2 表达水平以及血清素浓度的降低幅度随应激类型而变化。