Madaro Angelico, Fernö Anders, Kristiansen Tore S, Olsen Rolf Erik, Gorissen Marnix, Flik Gert, Nilsson Jonatan
Institute of Marine Research, NO, 5984 Matredal, Norway.
Department of Biology, University of Bergen, P.O. Box 7800, 5020 Bergen, Norway.
Physiol Behav. 2016 Jan 1;153:1-6. doi: 10.1016/j.physbeh.2015.10.002. Epub 2015 Oct 9.
The possibility to prepare for and respond to challenges in a proper manner is essential to cope with a changing environment, and learning allows fish to up or downregulate the stress response based on experience. The regulation of the response to predicted needs should be easier in more predictable environments. We exposed salmon parr to chasing of either 15 s (weak stressor) or 5 min (strong stressor) twice daily for a 7-day learning period, with chasing either announced by a 30 s light signal (conditioned) or not announced (unconditioned). The behavioural response to the light signal was different between the conditioned and unconditioned groups, demonstrating that conditioned groups associated the signal with chasing. We could, however, not demonstrate any effect on the stress response of anticipation. The fish habituated to repeated stress exposures with a similar decrease in oxygen hyperconsumption in all groups. Due to habituation, possible effects of predictable announcement of a stressor on the physiological stress response may not have been expressed in this study. Plasma cortisol concentrations 1h after light signal and chasing the day after the training period was moderate in all groups although higher after 5 min chasing (13 ng ml(-1)) than 15 s chasing (7 ng ml(-1)). There was no physiological stress response after exposure to the light signal only after the learning period. We argue that the benefit of predictability of stressors is limited when the fish have no way to avoid the stressor.
以适当方式应对挑战的能力对于适应不断变化的环境至关重要，而学习能让鱼类根据经验上调或下调应激反应。在更可预测的环境中，对应对预期需求的反应进行调节应该更容易。我们在为期7天的学习期内，每天两次让鲑鱼幼鱼分别接受15秒（弱应激源）或5分钟（强应激源）的追逐，追逐要么由30秒的光信号预告（条件性），要么无预告（非条件性）。条件性组和非条件性组对光信号的行为反应不同，这表明条件性组将该信号与追逐联系了起来。然而，我们未能证明预期对应激反应有任何影响。所有组的鱼都因习惯了反复的应激暴露而出现类似程度的氧过度消耗下降。由于习惯化，本研究中可能未体现出应激源可预测预告对生理应激反应的影响。训练期过后第二天，在光信号和追逐后1小时，所有组的血浆皮质醇浓度都处于中等水平，不过5分钟追逐后（13纳克/毫升）高于15秒追逐后（7纳克/毫升）。在学习期过后，仅暴露于光信号时没有出现生理应激反应。我们认为，当鱼类无法避免应激源时，应激源可预测性的益处是有限的。
