Pottinger T G, Mosuwe E
Institute of Freshwater Ecology, Windermere Laboratory, Far Sawrey, Ambleside Cumbria, United Kingdom.
Gen Comp Endocrinol. 1994 Sep;95(3):350-62. doi: 10.1006/gcen.1994.1133.
Postemergent salmonid fry experience a "critical period" in their development, during which there may be a high mortality rate, so determining the long-term success of the year class. The mechanism(s) underlying this phenomenon are not fully understood but physiological stress may be a contributory factor. This study sought to establish at what point in their development, posthatch, salmonids become stress responsive in terms of activation of the hypothalamic-pituitary-interrenal (HPI) axis. Immunoreactive corticosteroids were measured in tissue extracts of rainbow trout at intervals from 4 weeks prehatch to 27 weeks posthatch and in brown trout from 5 to 22 weeks posthatch. Corticosteroids were detectable throughout this period in both species. Simultaneous determination of whole-body immunoreactive corticosteroid levels (IRC) and plasma cortisol levels in fingerling trout validated the use of whole-body levels as an indicator of stress-induced elevation of corticosteroids. However, the dynamics of the circulating cortisol response to stress were not fully conveyed by whole-body measurements. From 5 weeks posthatch IRC increased significantly within 30-60 min following mechanical disturbance and confinement, suggesting a functional HPI axis to be present. An ectoparasite (Ichthyobodo sp.) infestation during this period caused a substantial increase in IRC levels in both species indicating that the HPI axis in these fish was sensitive to naturally occurring stressors. The response of fry to acute and chronic stress resembled that of adult fish in terms of duration. These data indicate that the early pre- and postemergent stages of salmonid fish are likely to be able to benefit from the adaptive advantage of HPI activation during episodes of acute stress but may also be susceptible to the deleterious consequences of prolonged activation of the HPI axis under conditions of chronic stress.
初孵鲑鱼幼鱼在其发育过程中经历一个“关键期”，在此期间可能有很高的死亡率，从而决定了当年鱼群的长期存活情况。导致这一现象的机制尚未完全明确，但生理应激可能是一个促成因素。本研究旨在确定鲑鱼在孵化后的发育过程中，下丘脑 - 垂体 - 肾间组织（HPI）轴激活时对压力产生反应的时间点。在孵化前4周直至孵化后27周的时间段内，每隔一段时间测量虹鳟鱼组织提取物中的免疫反应性皮质类固醇，对于褐鳟则在孵化后5至22周进行测量。在这两个物种的整个研究期间都可检测到皮质类固醇。同时测定幼鲑鱼的全身免疫反应性皮质类固醇水平（IRC）和血浆皮质醇水平，验证了将全身水平用作压力诱导皮质类固醇升高指标的可行性。然而，全身测量并不能完全反映循环皮质醇对压力反应的动态变化。孵化后5周起，机械干扰和限制后30 - 60分钟内，IRC显著增加，表明存在功能性HPI轴。在此期间，一种体外寄生虫（Ichthyobodo sp.）感染导致两个物种的IRC水平大幅上升，表明这些鱼类的HPI轴对自然发生的应激源敏感。幼鱼对急性和慢性应激的反应在持续时间上与成鱼相似。这些数据表明，鲑鱼幼鱼的早期孵化前和孵化后阶段可能能够从急性应激期间HPI激活的适应性优势中获益，但在慢性应激条件下，也可能易受HPI轴长期激活的有害影响。
