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<br />Ortder&,epoorlJ. ve, Re&., S6,67~71 (1989)
<br />THE USE OF ELECTRONARCOSIS AS ANAESTHETIC IN THE CICHLm.OREO-
<br />CHROMlS MOSSAMBICUS (PETERSk m. THE EFFECTS OF CHANGING ~ifySICAL
<br />AND ELECTRICAL PARAMETERS uN THE NARCOTIZING ABILITY uF HALF-
<br />W AVE RECTIFIED CURRENTS
<br />
<br />W. T. BARHAM<I), R.I. SCHOONBEE(2) and 1. G:' .J-. VISSER(1)
<br />
<br />ABSTRAcr
<br />BARHAM, W. T., SCHOONBEE, H. 1. & VISSER, 1. G. 1., 1989. The use of electronarcosis as
<br />anaesthetic in the cichlid, Oreochromis mossambicus (Peters). ill: The effects of changing physical and electri-
<br />cal parameters on the Jll!l'COtizing ability of half-wave rectified current. Onderstepoorf Journal of Veterinary
<br />Research. 56,67-71 (1989) .
<br />The narcotizing potential of various rectified current configuarations on Oreochromis mossambicus was
<br />investigated. A 50 Hz, 200 Vp. half-wave rectified current, applied for 30 s, was found to be a suitable
<br />configuration for electronarcosis.
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<br />INl'RODUcrrON
<br />
<br />Electronarcosis is a possible alternative to chemical
<br />anaes~esia for stress studies and routine handling proce-
<br />dures m freshwater fish (Barham, Schoonbee & Visser,
<br />1987 a,b). Although it is known that the Moore shocker,
<br />a rectified direct current unit designed for electrical fish-
<br />ing, induces narcosis (Moore, 1968), no detailed analy-
<br />sis of the narcotic effects of a half-wave rectified direct
<br />current is available. We have already reported on the
<br />narcotizing potential of alternating current (Barham et
<br />aI, 1987b) and this study, the third in the series, eval-
<br />uates the narcotizing potential of various rectified current
<br />configurations on die cichlid, Oreochromis mossam-
<br />bicus, using a modified Moore shocker.
<br />
<br />This information is necessary in order to complete the
<br />evaluation of Jherelevant physical effects of electro-
<br />-narcosis 01} this freshwater f!sh species. A comparison of
<br />the narcObC effects. of rectified current electronarcosis
<br />and alternating current electronarcosis will enable
<br />researchers to establish the most suitable narcosis
<br />procedures for their specific purposes.
<br />
<br />MATERIALS AND METHODS
<br />
<br />The materials and methods used in the present investi-
<br />gation are fully described in Part I of this series (Barham
<br />etal., 1987b).
<br />
<br />In this study the experimental groups of O. mossam-
<br />bicus each consisted of 8 acclimated fish and the electro-
<br />narcosis unit used was a Moore type shocker (Moore
<br />1968), as modified by Barham et al. (1987b). Output
<br />voltage was controlled by varying the input voltage of
<br />the unit by means of a variable transformer. In order to
<br />study the eff~t of electrical frequency it was necessary
<br />to vary the mput frequency of the shocker. This was
<br />achieved by using the output of the alternating current
<br />elec~narcosis unit described by Barham et al. (1987a)
<br />as the mput; Because of the output voltage limitations of
<br />the alternabng current apparatus the final rectified vol-
<br />tage used in the frequency studies was limited to 100 Vp.
<br />
<br />Exce}?t where otherwise stated the duration of current
<br />application was 30 s.
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<br />REsULTS i
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<br />Effects of voltage
<br />The. narcosis times of fish subjected to direct current
<br />potentials (Vp) of 100, 200, 300 and 350 V increased
<br />from a mean of 60,9 s at 100 V to a maximum of 137,4 s
<br />
<br />(I) Tilapia Research Unit, University of Zululand, Private Bag XlOOl,
<br />K wa Dlangezwa 3886 .
<br />(2) Research Unit for Fish Biology, Zoology Department, Rand
<br />Afrikaans University, P.O. Box 524, Johannesburg 2000
<br />Received 14 October 198B-Editor
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<br />at 200 V and then decreased somewhat at higher voltages
<br />although these decreases were not significant. The mean
<br />times at the three higher voltages were significantly
<br />(P = 0,01) or highly silUlificantly (P = 0,(01) greater
<br />than the mean time at 100 Vp. (Table I, Fig I). Narcosis
<br />coefficients showed similar trends.
<br />
<br />A mean opercular recovery time of 37.4 s at 100 Vp
<br />was the shortest and a potential of 200 Vp produced the
<br />longest time of 59,6 s, althouJili this figure was not signi-
<br />ficantlr greater than that resufting from the use of higher
<br />potentials.
<br />
<br />In contrast to these tendencies, recovery time
<br />
<br /> 200
<br />..
<br />'tl
<br />"
<br />0
<br />u
<br />.. 150
<br />..
<br />.!!
<br />..
<br />E
<br />;: 100
<br />..
<br />oiii
<br />0
<br />u
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<br />z 50
<br /> 0
<br /> 0
<br />
<br />f t f
<br />
<br />+
<br />
<br />100
<br />
<br />200
<br />
<br />300
<br />
<br />400
<br />
<br />Volts
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<br />FIG. 1 The effects of different peak potentials on mean narcosis times
<br />(:t SE) in 0: mossambicus subjected to rectified current
<br />electronarcosis
<br />
<br /> 300
<br />.. 250 "
<br />'tl
<br />"
<br />0
<br />u 200
<br />..
<br />..
<br />.!!
<br />" 150
<br />E
<br />;:
<br />.. 100
<br />.,.
<br />0
<br />~
<br />to 50
<br />z
<br /> 0
<br /> 0
<br />
<br />f
<br />
<br />+
<br />
<br />t
<br />
<br />5
<br />
<br />10
<br />
<br />15
<br />
<br />20
<br />
<br />25
<br />
<br />30
<br />
<br />Temperature DC
<br />
<br />FIG. 2 The effect of water temperature on the mean narcosis time (:t
<br />SE) in O. mossambicus subjected to rectified current electro-
<br />narcosis
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<br />67
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