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2 BIoLoGICAL REPORT 11 and Reynolds 1989), and the spatial charac- teristics of this energy are determined by a combi- nation of factors including the applied power, elec- trode configuration, and water conductivity. The effectiveness of any particular electrofishing unit can be changed significantly simply by modifying the electrodes even though the same measured voltage, current, or power may be applied. These differences occur because the geometric configura- tions of the individual electrodes in combination with their placement in the water define the shape, size, and distribution of the electrical power in the volume of water. For field operations, the electrical power can never be uniformly distributed in the water (Seidel and Klima 1974), and it becomes imperative to understand how the power is distrib- uted or concentrated near the electrodes. Studies of electric fields involve advanced engi- neering concepts, higher level mathematics, and the use of uncommon electrical terms. Biologists, whose only intent is to have a practical working knowledge of their equipment, may be discouraged by this degree of technical sophistication. Unfortu- nately, it is not possible to circumvent the technical jargon, but I describe procedures that will allow field biologists to actually measure and adequately design electrodes with common, inexpensive in- struments. The terminology, symbols, and equa- tions, as presented by Kolz (1989), are summarized in the Appendix. There are always two electrical barriers to in- terface when electroshocking fish. First, the elec- trical power must transfer from the electrodes into the water, and then, the power must transfer from the water into the fish. The singular concern addressed in this paper is the electrical power transfer from the metal electrodes into the water; no consideration is given to the mechanism of energy transfer into the fish (see Kolz and Reynolds 1989). Biologists can use this informa- tion to design, evaluate, adjust, and compare the characteristics of electrodes. Four aspects of elec- trode design are discussed: (1) measurements for determining electrode resistance, (2) circuit analyses of electrode arrays, (3) in-water voltage measurements, and (4) comparative data for spe- cific electrode configurations. All electrodes are assumed to be constructed with clean, smooth, high-conductivity metals without surface contamination or corrosion, no distinction is made between metals. DeMont (1971) compared the advantages of using specific metals in the construction of electrofishing elec- trodes. In practice, aluminum electrodes are popu- lar because of the variety of configurations avail- able at low cost, but stainless steel is recognized as being more durable. Measurement of Electrode Resistance The procedures necessary to measure electrode resistance in water are developed from basic cir- cuit theory, and the experimental techniques apply to any size or shape of electrode. This empirical method contrasts with the theoretical approach that is limited to only a few electrode configura- tions having known mathematic or graphic solu- tions (Novotny and Priegel 1974). Also, the book solutions often impose boundary conditions that are impractical for field applications and cause significant errors in the calculated values of elec- trode resistance. Electrical Theory Electrofishing systems all require a power source and a minimum of two electrodes. The two electrodes form a series circuit (Fig. 1). The elec- trodes can be treated in any analysis as discrete circuit components, and the total circuit resistance is the sum of the individual electrode resistances expressed in ohms. Thus, R(total) = (1) R(electrode 1) + R(electrode 2) ohms. In other words, standard circuit analysis tech- niques apply to electrofishing electrodes because a Current (1) Fig. 1. Basic electrical circuit for electrofishing equipment.