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4 BIOLOGICAL REpofa 11 V m 500 450 400 X3/500 300 250 200 150 100 50 .ti. r .................... .................... ..................... .................... Et ..........1.?.5.. • ................ ......................................... .•................ ..............\.`. L: .......... ................ ................ .................. ........... .... '•`• ... ... ................ .................. ................. .................. Y ??` '' •i., °• 'Diameter ???.......,?...:..? ........... ......................................... • .• ....•...... •-0.64 can ......inn • '?•.. •-1.27cm • ?..? ..?.~- 2.554 cm ............... - 6AB cm...... 0 20 40 60 80 100 Immersion depth of cylinder (centimeters) products are swept away by the movement of the electrodes through the water. Effects of Water Conductivity The measurement procedures determine an electrode's resistance for a specific value of water conductivity. When the electrode is submerged into water having a different conductivity, the elec- trode's resistance will change in inverse proportion to the two values of water conductivity. That is, R2 / Ri = ci / c2 (3) where R2 is the resistance of the electrode in the water having a conductivity equal to c2, and Rl is the resistance of the electrode in the original water having a conductivity of ci. Therefore, the resis- tance of an electrode can be calculated for any value of water conductivity once its resistance is experimentally determined for water of known conductivity. Measured Resistance Values for Metal Cylinders Figure 3 presents electrode resistance measure- ments for individual cylinders having outside di- ameters of 0.64, 1.27, 2.54, and 5.08 cm when suspended vertically to submerged cylinder lengths ranging from 15 to 80 cm in water having a conductivity of 100 microsiemerwem (µS/cm). For a cylinder length of 15 cm, these empirical results were almost 100% less than the theoretical Fig. 8. Individual electrode resistance values for cylinders in water having a conductivity of 100 µ$/cnL estimations (Novotny and Priegel 1974), and this difference decreases to less than 509/o with cylinder lengths of 80 cm. This error is predictable because the theoretical solution neglects the distortion cre- ated in the electrical field by the current conducted from the ends of the cylinders. This distortion becomes less significant as the cylinder length is increased. However, the magnitude of the error is more than might be anticipated for such a simple electrode and indicates why an experimental ap- proach is desirable and necessary for complex elec- trode configurations. Circuit Analysis Techniques for Electrode Arrays Commercially manufactured electrofishing ap- paratuses from the United States are designed as single phase, two-terminal systems. An electrode is wired to each of the two terminals of the power source via interconnecting electrical lines or leads. Often, additional electrodes are connected to either or both terminals of the power source to create an array of multiple electrodes. Every elec- trode attached to a given line is electrically con- nected in parallel with all other electrodes at- tached to the same line. The generic circuit for a two-terminal system having multiple electrodes is depicted in Fig. 4a for "M" electrodes attached to line A and "N" electrodes to line B. The series connection between the two parallel circuits (i.e.,