Electrical Threshold Parameters for Immobilization of Nile Tilapia

We subjected Nile Tilapia to uniform electrical fields to determine their effective conductivity, Cf, and their threshold power density for immobilization at match, Dm. Ambient conductivity values ranged from 5 to 500 µS/cm, and the fish averaged 25.9 cm TL. An ETS ABP-3 backpack was used to produce square-wave pulsed direct current of 120 Hz with a duty cycle of 25%. The calculated Cf was 27.4 µS/cm, and the Dm was 334 µW/cm³. These are the lowest Cf and highest Dm values for any fish tested thus far. We compared these results to data obtained from a similar study with Largemouth Bass. The Cf was 126 µS/cm and the Dm was 21.1 µW/cm³ for the bass which averaged 18.5 cm TL. The power transfer models for the tilapia and bass data were compared over a range of water conductivity. The ratio of voltage gradients required to produce immobilization increased with conductivity in a non-linear fashion. At the highest ambient water conductivity in which the models were compared, 500 µS/cm, Nile Tilapia required 7.2 times more V/cm for immobilization than did Largemouth Bass.