The body conductivity of fish (Cf; µS/cm) and the power density causing threshold immobilization (Dm; µW/cm³) play a critical role in determining electrofishing success. My aim was to compare two methods for estimating Cf and Dm: the response-threshold method using live Rainbow Trout Oncorhynchus mykiss (12–15 cm TL) and the direct-measure method using the carcasses of the same fish. The estimates were compared to values from other published studies. I also evaluated the effect of electric field constriction (e.g., depth effect) on Cf and Dm in tanks with water : fish cross-sectional area ratios of 6:1, 25:1, and 100:1. The resulting data conformed to theory for both methods; that is, Cf and Dm increased with decreasing tank size because field constriction forced more electric current through a fish. Estimates of Cf and Dm by both methods were similar in the two larger tanks (25:1 and 100:1). I suggest a standard Cf value of 60 µS/cm for Rainbow Trout if they are the target species. This value is near the low end of a cluster of published values for various fishes (50–160 µS/cm) that are within cross-sectional ratios of 20:1 to 100:1. A standard value for Dm cannot be recommended due to variation caused by electrical output and fish size and species. The direct-measure method proved superior to the response-threshold method because it requires fewer fish for estimates of Cf and Dm, does not depend on subjective determination of threshold in live fish, and provides information on water-to-fish power transfer efficiency.

中文翻译：

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估计鱼的身体电导率和固定阈值

鱼的身体电导率 ( Cf ; µS/cm) 和导致阈值固定 ( Dm ; µW/cm ³ )的功率密度在决定电钓成功方面起着关键作用。我的目的是比较两种估算Cf和Dm的方法：使用活虹鳟Oncorhynchus mykiss（12-15 cm TL）的响应阈值方法和使用相同鱼尸体的直接测量方法。将估计值与其他已发表研究的值进行比较。我还评估了电场收缩（例如，深度效应）对Cf和Dm 的影响在有水的水箱中：鱼的横截面积比为 6:1、25:1 和 100:1。结果数据符合两种方法的理论；也就是说，Cf和Dm随着水箱尺寸的减小而增加，因为场收缩迫使更多的电流通过鱼。两种方法对Cf和Dm的估计在两个较大的罐（25:1 和 100:1）中相似。如果虹鳟鱼是目标物种，我建议它们的标准Cf值为 60 µS/cm。该值接近已公布的各种鱼类 (50–160 µS/cm) 值的低端，这些值的横截面比为 20:1 到 100:1。Dm的标准值由于电力输出和鱼的大小和种类引起的变化，不能推荐。直接测量方法证明优于响应阈值方法，因为它需要更少的鱼来估计Cf和Dm，不依赖于活鱼阈值的主观确定，并提供有关水到鱼的功率传输效率的信息。