The effect of rapid and sustained decompression on barotrauma in juvenile brook lamprey and Pacific lamprey: Implications for passage at hydroelectric facilities

Fish passing downstream through hydroelectric facilities may pass through turbines where they experience a rapid decrease in pressure, which can lead to barotraumas including swim bladder rupture, exopthalmia, emboli, and hemorrhaging. 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. In fish lacking a swim bladder, such as lamprey, barotraumas due to rapid decompression may be reduced, however this has yet to be extensively studied. Another mechanism for barotrauma can be gases coming out of solution and the rate of this occurrence may vary among species. 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 s) or sustained decompression (17 min) to a very low pressure (13.8 kPa) using a protocol previously applied to juvenile salmon. No mortality or evidence of barotraumas was observed following rapid decompression, nor up to 120 h after sustained decompression. 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. Additionally, juvenile Chinook salmon experiencing sustained decompression died within 7 min. Thus, juvenile lamprey may not be susceptible to barotraumas associated with turbine passage to the same degree as juvenile salmonids.