Assessing barotrauma in neutrally and negatively buoyant juvenile salmonids exposed to simulated hydro-turbine passage using a mobile aquatic barotrauma laboratory

Barotrauma-injuries sustained following rapid decompression occur in many different fisheries applications. Previous attempts to quantify barotrauma in fish have been limited by the functionality of hypo/hyperbaric systems. Further, field studies often are confounded by covariates. The mobile aquatic barotrauma laboratory (MABL) was designed to address these limitations. Specifically, this testing facility allows the user to evaluate similar complex pressure scenarios to which migrating juvenile salmonids are exposed following turbine or spillway passage. In this paper, we describe the MABL and present a case study in which negative and neutrally buoyant juvenile Chinook salmon were exposed to simulated hydro-turbine passage (STP). The severity of the decompression profile and the fish's ability to gain neutral buoyancy were used as predictor variables. We determined that following STP, fish that achieved neutral buoyancy during a 16-h acclimation period had a greater risk of mortality and injury (gill emboli, swim bladder rupture, and internal hemorrhaging) than negatively buoyant conspecifics. This research solidifies the need to allow fish to become neutrally buoyant when assessing barotrauma and mortality in field and laboratory applications. Future research examining injury and mortality of turbine-passed fish needs to consider the fish's buoyancy to more appropriately evaluate these endpoints.