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<br />times
<br />
<br />E. F. 8LOUIN &. W. H. STOLTSZ
<br />
<br />TABLE 3 The effects of rectified current electronarcosis at 3 different water temperatures on opercular recovery, narcosis and recovery
<br />times respectively ._..- .
<br />
<br /> Opercular Narcosis
<br /> Length (em) Mass (g) recovery Narcosis time (s Recovery time (s) coefficient
<br /> , time (s) (s cm'l)
<br /> .... 8 8 8 . 8 8 8
<br /> n= -.
<br /> Minimum 31,2 532,5 68,8 92,2 10,3 ,.. 2,4
<br />~ Maximum , 43,2 1 285,4 99,9 156,5 63,4 4,0
<br />Range 12,0 752,9 31,1 64,3 53,1 1,6
<br />~ Mean 38,2 961,3 83,7 122,5 25,0 3,2
<br /> Standard dev. 4,4 273,3 14,2 27,5 22,0 0,6
<br /> Standard err. 1,9 122,2 6,4 12,3 9,8 0,3
<br /> . 8 8 8 8
<br /> n= 8 8
<br /> Minimum 25,1 910,4 40,7 56,4 5,2 1,4
<br />~ Maximum 40,7 1 059,6 64,3 156,1 12,8 4,5
<br />0 Range 15,6 149,2 23,6 99,7 7,6 3,1
<br />N Mean 33,7 1 008,0 52,4 99,0 8,6 3,0
<br /> Standard dev. 5,0 51,5 8,5 39,7 2,4 1,2
<br /> Standard err. 2,0 21,0 3,5 16,2 1,0 0,5
<br /> n= 8' 8 8 8 8 8
<br /> Minimum 31,5 539,1 30,1 44,4 12,7 1,2
<br /> Maximum , 59,2 1 266,2 48,9 154,3 110,0 4,1
<br />~ /
<br />on Range 27,7 727,1 18,8 109,9 97,3 2,9/
<br />N Mean .. 39,7 908,1 40,9 73,0 43,7 1,9
<br /> Standard dev. 8,8 238,5 5,9 34,3 35,7 0,9
<br /> Standard err. 3,1 84,3 2,1 12,1 12,6 0,3
<br /> 't' Values (df)
<br /> 15nO (14) NS NS 5,349 (P=O,OOI) NS 2,096 (P=O,05) NS
<br /> 15n5 (14) NS NS 7,872 (P=O,OOI) 3,184 (P=O,OI) NS 2,600 (P=O,02)
<br /> 20n5 (14) NS NS 3,143 (P=O,OI) NS 2,774 (P=0,02) 1,991 (P=O,I)
<br />
<br />s
<br />nt
<br />
<br />df = degree of freedom; P = two-tailed probability; NS = not significant
<br />
<br />.is
<br />ent
<br />')
<br />
<br />and rapid convulsive shudders of the body would
<br />commence a few seconds later. These movements
<br />made it extremely difficult to determine when the
<br />fish were responding to stimuli. On a number of
<br />occasions haemorrhaging of the gills was observed, a
<br />phenomenon which occurred in all the tests underta-
<br />ken on carp. In this respect the common carp dif-
<br />fered completely in its response to electronarcosis
<br />from that exhibited by the freshwater bream O. mos-
<br />sambicus, which recovered uneventfully.
<br />
<br />The effect of frequency
<br />
<br />A preliminary investigation showed that carp ex-
<br />hibited erratic opercular movements and convulsive
<br />shudders at frequencies ranging from 25 Hz to 500
<br />Hz, which made it difficult to determine the exact
<br />time of first response to a stimulus. Since there were
<br />no significant differences in opercular recovery
<br />times, narcosis times and recovery times in tilapia
<br />narcotized at different frequencies (Barham et a/.,
<br />1988), the effect of frequency on carp was not inves-
<br />tigated further.
<br />
<br />The effect of duration of application
<br />
<br />The results of duration of application time are pre-
<br />sented in Table 2. Current application was not ex-
<br />tended beyond a period of 60 s because of severe
<br />convulsions. Although mean narcosis times in-
<br />~reased with increasing application times up to and
<br />mcluding 45 s there was a slight but insignificant
<br />decrease when the current flowed for 60 s. This
<br />trend was not reflected in the mean narcosis coeffi-
<br />cients which did not increase significantly when ap-
<br />plication times exceeded 30 s. This indicates that the
<br />mcreased narcosis times observed at 45 sand 60 s
<br />application times were due to the increased sizes of
<br />the fish. Opercular recovery times reflected the nar-
<br />cosis coeffIcient pattern. The narcosis times for cor-
<br />
<br />responding current flows were in all instances sub-
<br />stantially lower in the common carp than the times
<br />observed for O. mossambicus.
<br />
<br />The effects of rectified current electronarcosis
<br />
<br />The effect of temperature
<br />
<br />Narcosis times declined with increasing water tem-
<br />peratures (Table 3, Fig. 2) but it was only the times
<br />at 15 oC and 25 oC that were si~nificantly different
<br />(P=O,OI). This trend was also eVIdent in mean oper-
<br />cular recovery times. Mean recovery times did not
<br />continue this trend and fish subjected to narcosis at
<br />20 OC recovered the quickest, followed by fish narco-
<br />tized at 15 oC, with those at 25 oC taking the longest
<br />time to recover. The narcosis coefficient decreased
<br />slightly as the temperature rose from 15 oC to 25 oC
<br />but decreased significantly at 25 oC (P = 0,02). Al-
<br />though carp exhibited a similar pattern to tilapia
<br />(Barham et al., 1988) the narcosis times for corre-
<br />sponding temperatures were much lower in the com-
<br />mon carp.
<br />
<br />DISCUSSION
<br />
<br />Electronarcosis suggests itself as a cheap and ef-
<br />fective alternative to chemical anaestheSIa and is
<br />free~rom the carcinogenic hazards often associated
<br />with cchemical anaesthesia. Barham et al. (1987b,
<br />1988, 1989) have shown that the tilapia O. mossam-
<br />bicus is an excellent candidate for electronarcosis,
<br />with an adequate period of narcosis and an unevent-
<br />ful recovery.
<br />
<br />The results obtained in this study clearly suggest
<br />that the common carp Cyprinus carpio is not a suit-
<br />able candidate for either alternating or rectified Cur-
<br />rent electronarcosis. The narcosis times induced are,
<br />generally, of too short a duration for practical use
<br />and the occurrence of haemorrhaging is a further
<br />
<br />217
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