Onukwufor John O, Wood Chris M
Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Comp Biochem Physiol A Mol Integr Physiol. 2018 May;219-220:10-18. doi: 10.1016/j.cbpa.2018.02.002. Epub 2018 Feb 14.
In the context of the osmorespiratory compromise, hypoxia and temperature have been little studied relative to exercise, and diffusive water flux rates (as assessed by HO efflux) have received almost no attention. We investigated the effects of fish size, hypoxia, exercise and acute temperature increase on diffusive water flux rates and net sodium loss rates in juvenile rainbow trout. Trout weighing 13-50 g were used to determine the effects of fish size under normoxia. Thereafter 25-50 g trout were selected to assess the effects of different hypoxia levels (3.15, 5.25 and 8.40 KPa), time course of hypoxia (1 h 8.40 KPa, 3 h 8.40 KPa, 1 h 8.40 KPa +1 h normoxic recovery, and 1 h 8.40 KPa + 3 h normoxic recovery), strenuous exercise (5 min) and acute temperature challenge (transfer from 8 °C to 13 °C or to 18 °C). Small fish (13 g) had higher diffusive water flux rates than larger fish, turning over >100% of their fractional body water pool per hour against 34% per hour for 50 g fish. Hypoxic exposure exerted a biphasic effect, increasing the diffusive water flux rate at 8.40 KPa and 5.25 KPa, while returning it to control levels at 3.15 KPa. All the levels of hypoxia increased net Na loss. One hour hypoxia (8.40 KPa) increased diffusive water flux rate while prolonged 3 h hypoxia (8.40 KPa), and short or prolonged normoxic recovery returned diffusive water flux rates to control levels. All the treatments over the time course of hypoxia and normoxic recovery increased net Na loss rates. Strenuous exercise increased both the diffusive water flux and net Na loss rates. Acute temperature rise increased diffusive water flux rates, with Q values of 4.03 for 8 to 13 °C and 2.16 for 8 to 18 °C, but the net Na loss rate did not change. There was no significant correlation between diffusive water flux rate and net Na loss rates at different hypoxia levels, over the course of hypoxia and normoxic recovery, or during acute temperature stress. In contrast, we observed a significant correlation between diffusive water flux and net Na loss rates following exercise. Overall, diffusive water flux and sodium loss were regulated differently during acute temperature challenge and hypoxia, while following exercise the two parameters were regulated in a similar fashion.
在渗透呼吸功能受损的背景下，相对于运动而言，低氧和温度方面的研究较少，而扩散水通量率（通过水外流评估）几乎未受到关注。我们研究了鱼的大小、低氧、运动和急性温度升高对虹鳟幼鱼扩散水通量率和钠净损失率的影响。使用体重13 - 50克的鳟鱼来确定常氧条件下鱼大小的影响。此后，选择25 - 50克的鳟鱼来评估不同低氧水平（3.15、5.25和8.40千帕）、低氧时间进程（8.40千帕1小时、8.40千帕3小时、8.40千帕1小时 + 常氧恢复1小时以及8.40千帕1小时 + 常氧恢复3小时）、剧烈运动（5分钟）和急性温度挑战（从8℃转移至13℃或18℃）的影响。小鱼（13克）的扩散水通量率高于大鱼，每小时其身体水分池的周转率超过100%，而50克的鱼每小时为34%。低氧暴露产生双相效应，在8.40千帕和5.25千帕时增加扩散水通量率，而在3.15千帕时使其恢复到对照水平。所有低氧水平均增加钠净损失。1小时低氧（8.40千帕）增加扩散水通量率，而3小时延长低氧（8.40千帕）以及短期或长期常氧恢复使扩散水通量率恢复到对照水平。在低氧和常氧恢复的时间进程中，所有处理均增加钠净损失率。剧烈运动增加扩散水通量率和钠净损失率。急性温度升高增加扩散水通量率，8℃至13℃时的Q值为4.03，8℃至18℃时为2.16，但钠净损失率未改变。在不同低氧水平、低氧和常氧恢复过程中或急性温度应激期间，扩散水通量率与钠净损失率之间无显著相关性。相比之下，我们观察到运动后扩散水通量与钠净损失率之间存在显著相关性。总体而言，在急性温度挑战和低氧期间，扩散水通量和钠损失的调节方式不同，而运动后这两个参数的调节方式相似。
