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

changes with temperature. At low temperatures (5°C} the resistivity of carp is very high,
requiring more electricity to drive a current through the fish. At warmer temperatures
(25°C) the carp's resistance is low and it takes less electricity to cause a response in the
fish. This is a little misleading, in fact, since the carp is a warmwater species. At
warmer temperatures, it is able to avoid an electrical field easier because it is at its
peak metabolically and physiologically. ~
Table 2. Effects of temperature on resistivity of carp (Adapted
from Whitney and Pierce 1957).
Temperature Fish Resistivity
°C
(ohm/crn)
5
10 2,690
15 1,840
2Q 1,400
25 975
508
Physiological condition. As seen with the carp-temperature example given above, the physio-
logical condition of a fish can affect its ability to be captured. If a fish has already
been stressed by some metabolic disturbance, it will not be able to escape as easily as if
it were a perfectly healthy fish in its normal environment. Many thi-ngs can cause the
physiological condition of a fish to change: the fish may have recently undergone stresses
associated with spawning, been exposed to toxic chemicals, or be in water that is of mar-
ginal quality because of temperature changes, pollution., or other factors. A freshwater
fish that-has been shocked is stressed and tends to lose ions to the water around it. It
takes awhile for that fish to recover and osmoregulate normally again. These features will
be discussed in greater detail elsewh~_ere in the paper.
To minimize the effects of electrofishing, and to insure that a healthy fish is returned to
the water after shocking, there are a couple simple things that can be done. Place the fish
in holding tanks containing a 1 1/2~ salt solution or a light anesthetic such as MS-222 or
quinaldine to reduce additional stressing.' The salt helps the fish replace lost ions and
the anesthetic slows the metabolism and helps to minimize any additional stresses that might
occur from holding or handling. Zt is also important that fish held for processing--are not
overcrowded or kept in poorly oxygenated waters.
Environmental Condit%ons. These factors are closely related to physiological condition.
en ~s are at t eir optimal temperature for instance, they are likely to be at their
peak physiologically and best able to escape an electrical field. A war'mwater species is
more adept at escaping in 25°C water than in 10°C water. If a fish is in a situation where
temperature i.s causing stress, electrofishing will capture that fish easily--but it may also
make that fish more susceptible to internal i~n~uries. A fish at its peak physiologically,
and in %ts favored habitat, will be more adept at avoiding electric fields. One example
that comes to mind is the northern pike. There are many contradictory reports in the liter-
ature concerning its ability to be captured by electrofishing (Vibert 1967, Novotny and
Priegel 1974, and Sternin et al. 1976). The difficulty in capturing this species is
probably due to a combination of factors: its excellent lateral line senses that enable it
to detect the presence of electrical fields or the approach of a boat; its natural habitat
of heavily vegetated waters that offer avenues of escape and may affect the size and
effectiveness of the electrical field; the pike's fusiform body, which reduces surface area;
and its swimming habits (.strong spurts of speed) which might carry it out of an electrical
field.
Seasonal climatic changes can also affect electrofishing by causing changes in water temper-
ature which greatly affect fish and conductivity of water. In addition, in late fall and
CAL-NEVA WILDLIFE.TRANSACTIONS 1984
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