OPTIMIZING ELECTRO-IMMOBILIZATION SETTINGS TO IMPROVE FISH WELFARE

Advances in technology and refinement of electro-immobilization techniques have led to specifically-designed equipment for immobilizing fish for handling, surgery, and other purposes. The effectiveness of electro-immobilization on fish depends on biological, environmental, and electrical variables. These variables may include: waveform type, applied voltage, frequency, pulse width, water conductivity, and fish size. The dynamic interaction among these variables can influence fish response, duration of immobilization, and incidence of traumatic injury in fish. The EA-1000B Electrosedation system is an electro-immobilization technology that is currently in operation at the Cowlitz Salmon Hatchery. This system has been shown to be more advantageous than the use of chemical sedatives for some situations; though fish excitation during the initial stages of electric exposure is a cause for concern from an animal welfare standpoint. During the excitation stage, fish exhibit an aversive behavioral reaction akin to a “flight” response—this behavioral response can be violent and may lead to injuries (e.g., broken vertebrae and hemorrhaging or bruising). Recent anecdotal evidence suggests that the excitatory period can be allayed by using different settings not currently available to the system. Accordingly, we evaluated potential new electro-immobilization settings for the EA-1000B Electrosedation system. The goal of this study was to identify an optimal setting effective at immobilizing fish while minimizing the excitatory period and associated trauma. Analysis of spinal injuries and hemorrhages are currently on-going.