From these data it appears that more » the majority of decompression related injuries are due to the expansion of existing bubbles in the fish, particularly the expansion and rupture of the swim bladder. This paper combines re-analysis of published data with new experiments to gain a better understanding of the mechanisms of injury and mortality for fish experiencing rapid decompression associated with hydroturbine passage. The mechanisms of these injuries can be due to expansion of existing bubbles or gases coming out of solution governed by Boyle’s Law and Henry’s Law, respectively. Fish passing by the turbine blade may experience rapid decompression, the severity of which can be highly variable and may result in a number of barotraumas. On their seaward migration, juvenile salmonids commonly pass hydroelectric dams. Thus, juvenile lamprey may not be susceptible to barotraumas associated with hydroturbine passage to the same degree as juvenile salmonids, and management of these species should be tailored to their specific morphological and physiological characteristics. Additionally, juvenile Chinook salmon experiencing sustained decompression died within 7 minutes, accompanied by emboli in the fins and gills and hemorrhaging in the tissues. In contrast, mortality or injury would be expected for 97.5% of juvenile Chinook salmon exposed to a similar rapid decompression to these very low pressures. No mortality or evidence of barotraumas, as indicated by the presence of hemorrhages, emboli or exopthalmia, were observed during rapid or sustained decompression, nor following recovery for up to 120 h following sustained decompression. In this study, juvenile brook and Pacific lamprey acclimated to 146.2 kPa (equivalent to a depth of 4.6 m) were subjected to rapid (<1 sec brook lamprey only) or sustained decompression (17 minutes) to a very low pressure (13.8 kPa) using a protocol previously applied to juvenile Chinook salmon. Another mechanism for barotrauma can be gases coming out of solution and the rate of this occurrence may vary among species. In fish that lack a swim bladder, such as lamprey, the rate and severity of barotraumas due to rapid decompression may be reduced however more » this has yet to be extensively studied. In juvenile Chinook salmon, the main mechanism for injury is thought to be expansion of existing gases (particularly those present in the swim bladder) and the rupture of the swim bladder ultimately leading to exopthalmia, emboli and hemorrhaging. These observations provide new opportunities to understand the pathways and effects of = ,įish passing downstream through hydroelectric facilities may pass through hydroturbines where they experience a rapid decrease in barometric pressure as they pass by turbine blades, which can lead to barotraumas including swim bladder rupture, exopthalmia, emboli, and hemorrhaging. Post-decompression photographs show that many internal injuries were visible and included hemorrhaging and the presence of emphysema within the body cavity and tissues.
High speed video recordings show the expansion of the swim bladder and subsequent release of gas through the mouth and gills, and into the body cavity when the swim bladder ruptured. Before and after photos were taken to review the injuries and high speed video allowed observations of barotrauma pathways in vivo. 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 noninvasively. However, it is difficult to see barotrauma occurring within the body of the fish in real time. The rapid decrease in pressure can cause barotrauma as undissolved gas expands according to Boyle’s law. During downstream passage of hydroelectric facilities, fish can be injured by rapid decompression this is especially noted during hydroturbine passage.
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