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

## TL;DR

This study examines how different fish species, especially cypriniforms, are affected by barotrauma during rapid pressure changes in hydropower turbines.

## Contribution

The study identifies species-specific injury patterns and swim bladder morphology as key factors in barotrauma sensitivity.

## Key findings

- Physostomous cypriniforms showed the highest sensitivity to barotrauma with frequent swim bladder ruptures.
- Depth acclimation increased vulnerability in European grayling.
- Partial load conditions in Kaplan turbines reduced barotrauma-related mortality.

## 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 with different swim bladder morphology to barotrauma using a custom-built chamber. Four different representative species, namely the two cypriniform species common nase (Chondrostoma nasus) and roach (Rutilus rutilus), both physostomous species with a two-chambered swim bladder, European grayling (Thymallus thymallus) as physostomous species with a single-chambered swim bladder and European perch (Perca fluviatilis) as physoclistous species with a single 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 physostomous cypriniforms showing the highest sensitivity and suffering frequent swim bladder ruptures. Depth acclimation, 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 barotrauma-related injury risks across species, particularly for species-rich groups like Cypriniformes and Characiformes that share similar swim bladder traits, to support sustainable hydropower development.

The online version contains supplementary material available at 10.1038/s41598-025-32670-y.