Electrical Conductivity as Applied to Electrofishing

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AbstractThe electrical power transferred from water to fish when electrofishing is related to the ratio between the electrical conductivity of the water and that of the fish. Measuring the conductivity of water is easily accomplished with a standard conductivity meter, but determining it for fish has been difficult. No other industry standard or biological methodology apparently requires knowledge of the electrical conductivity of an object or fish freely suspended in an electrified volume of water. Therefore, the technology associated with electrofishing is confronted with the dilemma of explaining the seemingly incompatible differences between the static, electrical conductivities measured for immobilized fish and the dynamic, effective conductivities observed with live fish. To resolve this conflict, a new parameter, immersion conductivity, is introduced, accompanied by a proposed technique to measure this parameter for fish or other conductive materials in electrified volumes of water. Electrical principles based on the maximum power theorem are applied to develop relationships between the size of the distorted electrical field surrounding an immersed material and the resultant values of immersion conductivity. The immersion conductivity for fish is demonstrated to be a function of the cross‐sectional area of the water volume relative to that of the fish contained therein; it is not a fixed value. Initially, inwater voltage gradient measurements are recorded for a rubber cylinder of known electrical conductivity to demonstrate the feasibility of the test protocol and produce appropriate power graphs. Immersion conductivity values of 72–204 μS/cm were then measured for sacrificed fish, and this range correlates with effective conductivity values previously reported for live fish. The protocol associated with the measurement of immersion conductivity determines the optimal water conductivity for maximum power transfer, thereby creating research opportunities for comparing the in vivo thresholds of electroshock response among different species of fish or different‐sized fish of the same species.