Can Cavitation Injure Fish?
bubbles, cavitation, herring, hydroelectric, injuries, mechanisms, pumps, turbines, fish passage
Innovations in Fish Passage Technology
American Fisheries Society
The scientific literature identifies several possible mechanisms (e.g. pressure flux, hydraulic shear, cavitation) through which hydraulic anomalies might lead to fish injuries. These are of interest with respect to the passage of fish through turbines and pumps. Of these, cavitation is undoubtedly the least well understood and is often down-played by engineers who take pride in designing hydraulic machinery to eliminate equipment damage due to cavitation. Biologists may argue, on the other hand, that fish are more delicate than turbo-machinery and therefore more susceptible to cavitation effects. In this study, the material properties of fish tissues were examined in relation to possible cavitation effects. A spark-gap apparatus was devised to generate single cavitation bubbles in proximity to the head and body surfaces of two species of fish (herring, Clupea harengus and sole, Solea solea). High-speed photography was used to form images of the development and collapse of the cavitation bubbles so-formed, and the fish were afterwards examined for signs of injury. Experimental controls used 2 mm brass plate in place of the fish. The findings demonstrate that cavitation bubbles can collapse onto the surface of a fish's body but do not necessarily cause injury. The risk of injury must be related to both the probability of a fish coming into contact or close proximity to a vapor cavity, and to the energy level associated with the cavity. It is unlikely that in the apparatus used the high energy levels associated with cavitation in a hydroelectric turbine were reached.