7119 ‎(2)‎

• UCREFRP Catalog Number: 7119
• Author: Emery, L.
• Title: Physiological effects of electrofishing.
• USFW Year: 1984.
• USFW - Doc Type: February 3-4, 1984.
• Copyright Material: NO

during winter months, many fish move into deeper waters where electrofishing equipment can-
not reach them. The spring may be the best time of the year to sample fish in temperate
regfions because many fish are moving into the warming shallower nearshore areas where they
are readily accessible to electrofishing. Electrofishing has been shown to be most effi-
d ent when used to sample small, shallow, clear water streams during low flow conditions.
Internal (physiological Effects of Electrofishing
A fish goes. through a number of 'different behavior patterns before it becomes fully
tetanized from electricity. Vibert's (1963) paper is one of the best references I've seen
for describing the reactions of fish in an electrical field. These reactions won't be
discussed in this paper, but the conditions created internally by fish reacting to these
currents are important clues as to how severely a fish may or may not be injured.
~~
There are many internal changes that can occur to a fish that has been electrofished. I
like to use the analogy of what happens to the long distance runner after running for a
period of time tb help understand what happens to a fish when it enters an electrical field.
After running for a certain distance, a runner builds up carbon dioxide in the bloodstream,
The muscles outpace the ability of the bloodstream to supply oxygen. As a result, lactic
acid accumulates in the muscles and interferes with their function. The muscles tighten up
or "tie up," fatigue sets in, and the runner cannot maintain his speed. This effect has
been labeled many names by running enthusiasts (e.g., the "wall," "balk," "tie-up," etc.),
but the end result is the same. For readers who are non-runners, and have experienced a
muscle cramp, the effects are from a lactic acid build-up. At any rate, a runner is unable
to resume his speed-until that build-up of lactic acid is removed from the bloodstream.
When a fish first comes into contact with an electrical field there is an increased res-
piratory action. Some researchers have even observed a violent coughing in the first 30 to
60 seconds after shockin has stopped (this fish is trying to get oxygen across the gills.
and into the 6loodstream~. Then, depending on its orientation in the field, there is a
series of rapid muscular contractions as the fish is drawn toward the anode. Like any
working muscle, these contractions cause a build-up of lactic acid and an increased oxygen
debt. As the fish undergoes a further depression of its motor activities, and is drawn
nearer the anode, it becomes impossible to ventilate or to remove the lactic acid and it
suffers an increased oxygen debt. The fish has just "worked" as hard as the runner.
In man, the blood lactate levels developed after exercise decline within one hour after the
exercise, but in fish, the decline in blood lactate to resting levels takes much longer (4
Ito 12 hours), This is probably due to the slower rate of diffusion of lactate across living
membranes at lower temperatures (Black 1958, Black et al. 1960),
Physiological monitoring of fish through blood chemistry studies are ways of monitoring
stress in fish. Schreck (1976) diagrammatically depicted several hypothetical levels or
adaptive stages that a fish goes through once it has been stressed (Figure 4). This
example can also be used to describe what happens to a fish when the stressor is an
electric .shock. The wiggly line in Figure 4 represents the normal oscillations of fish
under normal conditions. Once a stressor, in this case an electric shock, is applied, the.
fish i-nmediately responds to that stressor through an alarm response. There is an internal
resistance to that alarm. The fish has a choice of moving out of the electrical field or
suffering the consequences. One of the physiological consequences of this stressor is that
the rapid contraction of muscles causes a build-up of lactic acid in the blood. What can a
fish do now that it has changed its physiological state? Several things can occur. As
Schreck (_1976) has shown, the fish can go through several levels or adaptive stages during
which time it will either recover (adapt) or die. If the shock has not been too severe
(severity is directed related to the total electrical energy absorbed by the fish and to
the length of time spent in the field), the fish recovers after a period of time and returns
to normal (line 2). There may be a period of time after the shock that the fish remains
quiet, rests on the bottom, or.is compensating for the energy absorbed, but has not quite
recovered to normal (line 1). After a while., it too recovers to normal. If the fish can't
compensate, i.t might end up in one of the other hypothetical stages (lines 3-5). In these
stages, blood lactate has increased to such a level that the fish either adapts or dies.
Once the lactic acid reaches a certain level in a fish (e.g. line 5), it may be unable to
CAL-NEllq WILDLIFE TRANSACTIONS 1984
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