Fish scale-loss caused by simulated hydraulic shear stress

Riverine fishes found within streams impacted by hydropower also often pass through hydropower turbines during annual downstream migrations. During turbine passage events, fish may experience a suite of stressors including rapid pressure changes, impacts from turbine blades, and exposure to hydraulic shear. Scale-loss is often observed in fish collected below dams and hydraulic shear is the most likely cause of this trauma. While exposure to shear may cause other injuries, scale-loss appears to be the most common non-lethal injury observed to date. We sought to quantify how hydraulic shear may cause scale-loss in rainbow trout, gizzard shad, and hybrid striped bass by precisely controlling the exposure level (velocity) and duration (seconds) of a water jet. We targeted the same area for all three species found between the operculum and dorsal fin on the left, lateral surface. Exposure velocities ranged from 0 (controls) to 11.0 meters/second but fish were only exposed to the water jet for 1.5 seconds. A 0.2 milligram/milliliter solution of fluorescein was used to stain the areas of scale-loss by submerging each fish in this solution for at least 6 minutes. Fluorescein was used because it interacts with epithelial tissue that has been damaged and it fluoresces under ultraviolet lighting. Fish were photographed under short- and longwave ultraviolet lighting in a dark chamber to capture fluorescence. Fish photographs were analyzed using ImageJ and the proportion of descaled area was estimated for each fish within a 35 by 35-millimeter square. In general, these data highlight how exposure to hydraulic shear may lead to significant levels of descaling in riverine fishes.栖息于受水电开发影响溪流中的淡水鱼类，在年度下游洄游过程中往往会途经水力发电涡轮机。在涡轮机通行过程中，鱼类会遭遇一系列胁迫因素，包括压力骤变、涡轮叶片撞击以及水力剪切（hydraulic shear）暴露。在大坝下游采集的鱼类身上常可见鳞片脱落现象，而水力剪切被认为是造成该损伤的最可能诱因。尽管剪切暴露可能引发其他损伤，但迄今为止，鳞片脱落是被观测到的最常见非致死性损伤类型。 本研究旨在通过精准控制水射流的暴露强度（流速）与暴露时长（秒数），量化水力剪切对虹鳟（rainbow trout）、美洲真鰶（gizzard shad）及杂交条纹鲈（hybrid striped bass）造成鳞片脱落的作用机制。针对三个物种，我们均选取左侧体侧鳃盖骨与背鳍之间的同一区域开展实验。水射流的暴露流速范围为0（对照组）至11.0米/秒，且所有鱼类的暴露时长均为1.5秒。 我们使用浓度为0.2毫克/毫升的荧光素（fluorescein）溶液对鳞片脱落区域进行染色：将每条鱼浸入该溶液中至少6分钟。选用荧光素的原因在于，其可与受损上皮组织结合，并在紫外光照下发出荧光。实验在暗室中使用短波与长波紫外光对鱼类进行拍摄，以捕获荧光信号。随后使用ImageJ软件对鱼类照片进行分析，并在35×35毫米的正方形区域内估算每条鱼的脱鳞面积占比。 总体而言，本数据集揭示了水力剪切暴露可导致淡水鱼类出现大面积脱鳞现象。