7784

• UCREFRP Catalog Number: 7784
• Author: Snyder, D. E.
• Title: Impacts of Electrofishing on Fish.
• USFW Year: 1992.
• USFW - Doc Type: \
• Copyright Material: NO

8 Review I Electric Fields in Water

of data, and avoid unnecessary replication of effort.
The foundation for such a coordinated effort is a
synthesis of what we already know or suspect.
The following synthesis concentrates primarily
on the effects of electric fields on fish, particularly
injurious and fatal effects, and on various controlling
factors. Suggestions for minimizing injurious effects
and mortality based on existing infOJmation are
summarized under conclusions and recommendations.

ELECTRIC FIELDS IN WATER

Electrofishing (sometimes referred to as electric
or electrical fishing, electroshocking, or simply
shocking), as well as the use of electrical barriers,
screens and some fOJms of anesthesia, depend on the
. generation of a sufficiently strong electric field
around electrodes in water to elicit the desired
responses by targeted fishes. The size, shape, and
electrical intensity of that field are determined largely
by container or basin configuration and dimensions;
conductivity of the water and bounding or
interspersed substrates; size, shape, and position of
the electrodes; and the power and form of current
applied through the electrodes. These factors are
discussed extensively by Cuinat (1967), Novotny and
Priegel (1971, 1974), HaIsband and HaIsband (1975,
1984), Stemin et al. (1972, 1976), Smith (1989), and
Novotny (1990).

Impacts of Electrofishing on Fish

Water Conductivity

Water conductivity, its capacity to conduct an
electric current, is the most critical environmental
factor in defining the strength and range of an
electrofishing field. The conduction of electricity in
water is an ionic phenomena. Conveyance of
electrons from negative to positive electrodes
(cathode to anode) to complete an electrical circuit
depends on electrolytic reactions at the electrodes
and an almost instantaneous chain of ionic
movements and interactions in the water between and
around the electrodes. Accordingly, conductivity
varies directly with ionic content, the dissolved
solids, salinity, alkalinity, and pH of water. In
nearly pure water which has a very low conductivity,
ionization of water itself fumishes a substantial
portion of the conducting ions. When electrofishing
in very low-conductivity streams, some biologists
have found it necessary to artificially increase
conductivity by adding salt to water upstream of the
sampling area (Lennon and Parker 1958; Zalewski
and Cowx 1990). Conductivity is the reciprocal of
resistivity (ohms-cm), a term preferred by some
authors, especially for very low-conductivity (high-
resistivity) waters. Conductivity is usually measured
with a conductivity meter as mhos or siemens (S) per
em (usually J.1IDhos/cm or J,LS/em; J,L = micro or 10-6;
mho is ohm spelled backward to indicate the inverse

Figure 4. Brands (bruises) in rainbow trout caused by electrofishing. Brands are usually a temporary
external manifestation of spinal injury, but injured fish often lack brands. (photograph provided by and
reproduced with the permission ofW. A. Fredenberg).

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