Sensitivity of larval and juvenile fish with different swim bladder morphology to barotrauma with a special focus on Cypriniformes

Abstract Barotrauma, caused by rapid pressure changes, poses a major risk to fish migrating downstream through hydropower turbines. This study investigated the sensitivity of larval and juvenile fish to barotrauma with different swim bladder morphology to barotrauma using a custom-built chamber. Four different species, namely European grayling (Thymallus thymallus) as physostomous species with a single-chambered swim bladder, European perch (Perca fluviatilis) as physoclistous species with a single chambered swim bladder, common nase (Chondrostoma nasus) and roach (Rutilus rutilus), both physostomous species with a two-chambered swim bladder were investigated. Fish were acclimated to 0- or 15-meters depth (101 and 251 kPa, respectively) and exposed to rapid decompression to different nadirs (15, 30, 40, 60 kPa) to simulate turbine passage as a basis to construct dose-response curves predicting lethal injury probabilities. Species- and stage-specific injury patterns emerged, with phyostomous cypriniforms suffering more frequent anterior swim bladder ruptures. Depth acclimatization, particularly in E. grayling, increased vulnerability. Moreover, lower barotrauma-related mortality was observed under partial load conditions in Kaplan turbines compared to full load. These insights are of high relevance for predicting injury risks across species, particularly for species-rich groups like Cypriniformes and Characiformes that share similar swim bladder traits, to support sustainable hydropower development.