Using transparent fish to observe barotrauma associated with downstream passage through hydropower turbines

During downstream passage at hydroelectric facilities, fish can be injured when exposed to rapid decompression; this is especially of concern when passing through turbines. The rapid decrease in pressure can cause barotrauma, as undissolved gas expands according to Boyle's law. However, it is difficult to see barotrauma occurring within the body of the fish in real time. In order to determine if transparent fish could provide greater insight into barotrauma, five species of transparent tropical fish were exposed to rapid decompressions so internal injuries could be viewed without causing further damage to the fish. Before and after photos were taken to review the injuries and high-speed video allowed observations of barotrauma pathways in vivo. High-speed video recordings showed the expansion of the swim bladder and subsequent venting of gas through the mouth and gills, and, when swim bladder rupture occurred, the expulsion of gas into the body cavity. Post-decompression photographs show that many internal injuries were visible and included hemorrhaging and the presence of free intraperitoneal gas within the body cavity and tissues. These observations provide new opportunities to understand the effects of downstream passage through hydropower turbines and the pathways and effects of barotrauma in fish.