CCMAR-CIMAR L.A., Centre of Marine Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
Fish Physiol Biochem. 2013 Jun;39(3):479-87. doi: 10.1007/s10695-012-9713-2. Epub 2012 Sep 15.
The existence of daily rhythms under light/dark (LD) cycles in plasma cortisol, blood glucose and locomotor and self-feeding activities, as well as their persistence (circadian nature) under constant light (LL), was investigated in Senegalese sole (Solea senegalensis). For the cortisol and glucose rhythms study, 48 soles were equally distributed in 8 tanks and exposed to a 12:12 LD cycle and natural water temperature (experiment 1). After an acclimation period, blood was sampled every 3 h until a 24-h cycle was completed. Blood glucose levels were measured immediately after sampling, while plasma cortisol was measured later by ELISA. In experiment 2, the fish were exposed to LL for 11 days, and after this period, the same sampling procedure was repeated. For the study of locomotor and self-feeding rhythms (experiment 3), two groups of sole were used: one exposed to LD and the other to LL. Each group was distributed within 3 tanks equipped with infrared photocells for the record of locomotor activity, and self-feeders for feeding behavior characterization. The results revealed a marked oscillation in cortisol concentrations during the daily cycle under LD, with a peak (35.65 ± 3.14 ng/ml) in the afternoon (15:00 h) and very low levels during the night (5.30 ± 1.09 ng/ml). This cortisol rhythm persisted under LL conditions, with lower values (mean cortisol concentration = 7.12 ± 1.11 ng/ml) and with the peak shifted by 3 h. Both rhythms were confirmed by COSINOR analysis (p < 0.05). The synchronizing role of temperature and feeding schedule, in addition to light, is also discussed. Diel rhythms of glucose were not evident in LD or LL. As to locomotor and self-feeding activity, a very marked rhythm was observed under LD, with higher activity observed during the night, with acrophases located at 2:14 and 3:37 h, respectively. The statistical significance of daily rhythms was confirmed by COSINOR analysis. Under LL, both feeding and locomotor rhythms persisted, with an endogenous period (τ) around 22.5 h. In short, our findings described for the first time the existence of circadian cortisol and behavioral circadian rhythms in flat fish. Such results revealed the importance of taking into account the time of day when assessing stress responses and evaluating physiological indicators of stress in fish.
本研究旨在塞内加尔鳎（Solea senegalensis）中探索血浆皮质醇、血糖和运动及自主摄食活动在光/暗（LD）周期下的日节律的存在及其在持续光照（LL）下的持续性（昼夜节律性质）。在皮质醇和葡萄糖节律研究中，将 48 条鳎鱼平均分配到 8 个水箱中，并暴露于 12:12 LD 周期和自然水温下（实验 1）。经过适应期后，每 3 小时采样一次，直到完成 24 小时周期。采样后立即测量血糖水平，然后通过 ELISA 测量血浆皮质醇。在实验 2 中，鱼被暴露于 LL 11 天，在此期间后重复相同的采样程序。在运动和自主摄食节律的研究（实验 3）中，使用两组鳎鱼：一组暴露于 LD，另一组暴露于 LL。每组分布在 3 个配备红外光电管的水箱中，用于记录运动活动，并对自主摄食行为进行特征描述。结果表明，在 LD 下的日常周期中，皮质醇浓度有明显的波动，下午（15:00 小时）达到峰值（35.65±3.14ng/ml），夜间水平非常低（5.30±1.09ng/ml）。这种皮质醇节律在 LL 条件下持续存在，但其值较低（平均皮质醇浓度=7.12±1.11ng/ml），峰值滞后 3 小时。这些节律均通过 COSTNOR 分析得到确认（p<0.05）。此外，还讨论了温度和喂养计划除光以外的同步作用。在 LD 或 LL 下，血糖的昼夜节律不明显。至于运动和自主摄食活动，在 LD 下观察到非常明显的节律，夜间活动较高，峰相位分别位于 2:14 和 3:37 小时。COSTNOR 分析证实了每日节律的统计学意义。在 LL 下，摄食和运动节律持续存在，内源性周期（τ）约为 22.5 小时。总之，本研究首次描述了扁鱼中昼夜皮质醇和行为昼夜节律的存在。这些结果表明，在评估鱼类的应激反应和评估应激生理指标时，考虑一天中的时间非常重要。
