7129

• UCREFRP Catalog Number: 7129
• Author: Barham, W. T., H. J. Schoonbee and J. G. J. Visser
• Title: Use of Electronarcosis as Anesthetic in the Cichlid,
• USFW Year: 1989
• Copyright Material: YES

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It is interesting to note from Table 4 and Fig. 4 that,
although the mean lJpetcular recovery time is somewhat
shorter at 200 Hz than at SO Hz, this is not the case for
narcosis times, where there was no sianJt1c:ant difference
between the duration of narcosis at SO Hz and at 200 Hz.
In contrast, while mean opercular recovery time at 100
Hz did not differ significantly from the time at the other
frequencies, the mean narcosis time at this frequency
was significantly longer (P = 0,02) than at either SO Hz
or 200 Hz. At 4,0 s cm-I the narcosis coefficient for 100
Hz was also somewhat higher than for either of the other
two frequencies.

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DISCUSSION

In the past no clear distinction was 'made between
narcosis induced br an electric current and paralysis
caused by an electric current. In the case of paralysis a
fish will swim away as Soon as the current is SWItched
off. Where true narcosis is induced the fish will remain
immobilized and relaxed for a period after the current is
disconnected. In the present series true narcosis was
always indUCed-by all the electrical configurations used,
the fish remaining limp and unresllOnsive for varying
periods after the current had been SWItched off.

The results show that a half-wave rectified current will
induce narcosis in the freshwater bream O. mossambicus
and that a potential of 200 Vp is adequate to produce a
sustained narcosis for 140 s. This compares favourable
with the 156,8 s produced by a 60 Vrms, SO Hz, sine
wave current (Barham et ai., 1988). Although a fre-
quency of 100 Hz produced the longest narcosis times,
the results achieved at 50 Hz are adequate and more
practical in terms of unit design.

The effecrof water temperature on narcosis times is in
agreement with that. obtained for alternating current
(Barham et ai., 1988) and may perhaps be due to tempe-
rature induced changes in the cell membranes.

The decrease in mean narcosis time after 60 s of cur-
rent application is in general agreement with the results
observed by Barham et ai., (1988) for alternating cur-
rent. The reason for this phenomenon is not clear. Fur-
ther investigation into this aspect will no doubt prove
fruitful.

This series, consisting of three parts studying the nar-
cotic effects of electro-anaesthesia, has shown that fish
length. is an ~portant consideration in detennining the
narcotic potenbal of an electrical CUJ1'ent in the tilapiine
fish O. mossambicus.

The narcotic coefficient derived from the ratio of nar-
cosis time to fish length (Barham et ai., 1987b) can be a
useful tool in predicting the duration of narcosis for a
given size of fish. Further refinement of this formula

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W, T. 8ARHAM, H. J. SCHOONBBE It. J. O. J. VISSBR

involving a biological constant should make these pre_
dictions more accurate. "~
Variations in o~lar times and recovery times for
both alternating and rectified currents would not nor-
mally be major considerations in evaluating narcotic
potentials. The actual period of narcosis must be the
major criterion ,when evaluating the narcotic effects of an
electric current.
In contrast to chemical anaesthesia using benzocaine
hydrochloride, where recovery from aneasthesia ap~
traumatic, with the fish undergoing periods of VIolent
swimming activities (personal observation), recovery
from both forms of electronarcosis studied appears
uneventful.
This series of investigations has clearly shown that
both alternating and rectified current electronarcosis pr0-
duced adequate periods of anaesthesia in O. mossam-
bicus for most routine laboratory procedures. AlthouJili
an elaborate alternating current umt was employed in the
study, a 60 Vrms, 50 Hz or similar current can usually be
be obtained in most laboratories, using the main supply
and a suitable transformer. It must be emphasized in the
interests of operator safety that electronarcosis units, in /
~ instances, must be isolated from the main supply.
'this configuration should be within the means of most
laboratories. In contrast, a rectified current electro-
narcosis unit requires a more elaborate system.
Thus, based on a consideration of the narcotic effects
obtained and with due consideration to the circuit practi-
calities, alternating current electronarcosis at 60 Vrms,
50 Hz, appears to be the electronarcosis procedure of
choice for O. mossambicus.

ACKNOWLEDGEMENTS
The financial assistance of the University of Zululand
and the Rand Afrikaans University is gratefully acknowl-
1 edged.
REFERENCES
BARHAM. W. T., ScHooNBEE. H. 1. & VISSER, 1. G. J., 1987a. The
design and development of an alternating current electronarcosis unit
/ for use with freshwater fish. University of Zululand Publications.
Series B. 20 pp.
BARHAM, W. T., SCHooNBEE, H. J. & VISSER, J. G. 1., 1987b. The
use of electronarcosis as anaesthetic in the cichlid Oreochromis mos-
sambicus (Peters). I. General experimental procedures and the role
of fish length on the narcotizing effects of electric currents.
Onderstepoort Journal of Veterinary Research, 54, 6l7~22.
BARHAM. W. T., SorooNBEE. H.l. & VISSER, 1. G.l., 1988. The use
of electronarcosis as aneasthetic in the cichlid Oreochromis mossam-
bicus (Peters). II..The effects of changing fhysical and electrical
parameters on the narcotizing ability 0 alternating current.
Onderstepoort Journal of Veterinary Research, 55, 205-215.
MOORE. W. H., 1968. A light-weight pulsedd.c. fish shocker. Journal
of Applied Ecology,S, 205-208.

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