Optimal AC frequency range for electro-stunning of Atlantic salmon (Salmo salar)

The objective of this study was to verify the optimal AC frequency range to be used during industrial electrostunning, i.e. electro-narcosis, of Atlantic salmon (Salmo salar) by investigating the electrical impedance spectra of the combined fish and electro-stunning device entity. The electrical impedance and appurtenant phase shiftwasmeasured in the frequency range 40 Hz to 1.0MHz for individual fish (n=11) placed in a regular electrical stunner. The results of the experiment show that the average overall impedance of the combined fish and electrical stunning device increases with frequency from 40 to 60 Hz before leveling out in the range from 60 to 800 Hz. Thereafter the impedance decreases to a negligible value at 1 MHz. Measurements on impedance and phase angle show that the highest average electrical impedance is at 100 Hz. Furthermore, there are individual peak impedance variations between 70 and 100 Hz. In all fish measured, the impedance at 900 Hz was observed to be lower than that at adjacent frequencies. Due to the measured average impedance values, and the expected influence of the alpha dispersions on the cell surface as reported in previous research, it is concluded that the optimal AC frequency range for electro-stunning of the Atlantic salmon brain is 70 to 100 Hz. Statement of relevance: • Electrical stunning is widely used within the Aquaculture and fisheries industry. Therefore it is important to find the optimal frequency for electrical stunning based on the electrical property of the fish. • No one has investigated the electrical property of the fish related to electro-stunning and thereby verified the optimal frequency based on the electrical impedance. • This is the first article that shows the connection between the electrical impedance spectrum of biological tissue and the stunning efficiency of Atlantic salmon.