Dynamic behaviour of fish with swim bladders subjected to underwater explosions and methods for mitigating injuries

Underwater blasting activities such as reef excavation and offshore mining inevitably affect aquatic organisms, particularly fish. However, few studies have focused on damage induced by underwater explosions on nearby fish. In this study, underwater explosion experiments were conducted to investigate the effects of water shock waves on crucian carp injuries. By comparing the cosmetic damage and mobility of the fish before and after the explosion and combining the anatomical results with the peak pressure at the location of the fish, the specific damage mechanisms of underwater explosions on fish were comprehensively analysed. Additionally, a numerical model based on the fluid–solid coupling method was developed to study the dynamic behaviour of fish subjected to underwater explosions. Finally, the attenuating effect of bubble curtains on the propagation of the water shock wave was analysed. Rupture of the swim bladder was found to be the primary cause of fish mortality. The critical peak pressure for swim bladder rupture was determined as 9.8 MPa. Based on the peak pressure obtained from experiments and autopsy results, the injury grades were meticulously categorised as follows: no injury for pressures below 3.2 MPa, slight injury for pressures of 3.2–5.2 MPa, moderate injury for pressures of 5.2–7.5 MPa, serious injury for pressures of 7.5–9.8 MPa, and extremely serious injury for pressures over 9.8 MPa. Furthermore, under the protection of a bubble curtain, the peak pressures at the two measurement points for crucian carp in the experiment significantly decreased from 13.5 MPa and 6.7 MPa to 2.4 MPa and 0.6 MPa, respectively. The degree of fish injury changed from extremely serious and serious injuries to no injury, demonstrating that bubble curtains serve as an effective mitigation measure to reduce the impact of underwater explosions on fish.