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<br />> 4 <br /> <br /> <br />i <br />I <br />I <br />I <br />J <br />.~ <br /> <br />i q ~ ~ DM-h Mn) er aJ <br /> <br />OnderSlepoort J. vet. Res., '6, 21s-.218 (1989) <br /> <br />/( r Utsser- <br /> <br />u7Id~.. <br /> <br />RESEARCH COMMUNICATION <br /> <br />SOME OBSERVATIONS ON THE NARCOTIZING ABILITY OF ELECTRIC CURaENTS <br />ON THE COMMON CARP CIT;~INUS CARPIO . <br /> <br />I W. T. BARHAM!, H. J. SCHOONBEE2 andJ. G. J. VISSER! <br /> <br />ABSTRAcr <br />BARHAM, W. T., SCHOONBEE, H. J. & VISSER, J. G: J., 198~. Some observations on the <br />narcotizing ability of electric currents on the common carp Cyprmus carpiO. Onderstepoort Journal of <br />Veterinary Research, 56,215-218 (1989). <br />Some effects of alternating current electronarcosis and ?f rectified currc:nt electronar~sis on C. <br />carpio were investigated. In alllOstances recovery from narcosIs was accompamed by convulslv~ spasms. <br />Haemorrhaging of the gills was also observed to occur. Carp do not appear to be sUitable candIdates for <br />electronarcosis. <br /> <br />INTRODUCTION <br /> <br />The European common carp Cyprinus carpio is <br />one of the most domesticated freshwater fish used in <br />aquaculture today. Although the pond production of <br />tilapia is still on the increase in countries such as <br />Taiwan and Israel (Schoonbee, personal observa- <br />tion, 1988) the common ca9' still remains an impor- <br />tant table fish in the Mediterranean and northern <br />European countries. Even in Israel where pond pro- <br />duction of tilapia has increased significantly from. <br />5 % of the total pond fish yield in 1967 to almost <br />27 % in 1987 (Sarig, 1987), the common carp still <br />comprises more than 60 % of the total tonnage of <br />pond fish produced. For this reason research on its <br />feeding and reproduction biology is still continuing <br />(Viola & Arieli, 1983; Siwicki & Studnicka, 1986; <br />Viola, Arieli & Zohar, 1988). <br /> <br />C. carpio is known to survive water temperatures <br />well below 10 oC but can also withstand wann water <br />conditions exceeding 30 oC (Schoon bee, personal ob- <br />servation, 1972). It has a tough leathery skin richly <br />endowed with mucus cells and has been subjected to' <br />a number of blood PhYSiOlogic. al studies locally (Fer- <br />reira, 1979, 1982; Smit, 1980). <br /> <br />Barham Schoonbee & Visser (1987b, 1988, 1989) <br />reported on the narcotizing effects of electric Cur- <br />rents on the tilapia Oreochromis mossambicus and <br />came to the conclusion that alternating current was <br />the method of choice for that species. The present <br />study evaluates the use of both alternating and recti- <br />fied currents on C. carpio as possible alternatives to <br />chemical anaesthesia. <br /> <br />MATERIALS AND METHODS <br /> <br />The materials and methods were those used by <br />Barham et al. (1987a,b, 1988, 1989). Fish were elec- <br />tronarcotized individually in a 60 cm long 48 t ca- <br />pacity aquarium. Water temperature was 20 oC un- <br />less otherwise indicated. Alternating current electro- <br />narcosis was induced at a potential of 60 Vnns, ex- <br />cept in the voltage trials. Rectified current <br />electronarcosis was induced at a potential of 100 Vp. <br />Each group consisted of 8 fish. <br /> <br />RESULTS <br /> <br />The effects of alternating current electronarcosis <br /> <br />The effects of voltage <br /> <br />Although there was a significant difference (P = <br />0,01) in mean narcosis times between 15 Vnns and <br /> <br />1 Tilapia Research Unit, University of Zululand, Private Bag <br />X1001, KwaDlangezwa 3886, Republic of South Africa. <br /> <br />2 Department of Zoology, Rand Afrikaans University, P.O. Box <br />524. Johannesburg 2000, Republic of South Africa. <br /> <br />Received 6 March 1989-Editor <br /> <br />30 Vnns and highly significant differences (P = <br />0,001) in the mean narcosis time at 15 Vnns and the <br />mean times obtained at 60 Vnns and at 90 Vnns, the <br />mean narcosis times at 30, 60 and 90 Vnns did not <br />differ significa,ntly from each other (T~ble 1, Fi~. 1). <br />This pattern 1S remforce~ by narcOSIs co~fficlents <br />which show clearly that, WIth a m~an narcosIS coeffi- <br />cient value of 1,2 s cm- , a potenttal of 15 Vnns was <br />the least effective voltage. Furthe~ore an incr~ase <br />in the potential beyond 30Vnns dldnot resul~ m a <br />substantial improvement on 2,1 s cm-!. The higher <br />voltage also resulted in longer opercular r~covery <br />times than at the lowest voltage but once agam there <br />were no significant differences in these times at the <br />higher voltages. This pattern extended to recovery <br />times. <br />At all voltages the fish exhibited erratic opercular <br />movements shortly after the current was switched off <br /> <br />200 <br /> <br />OJ <br />-g 150 <br />o <br />" <br />'" <br />"' <br />.S <br />"'100 <br />~ <br />OJ <br />'w <br />o <br />~ <br />.. 50 <br />Z <br /> <br />t <br /> <br />t <br /> <br />* <br /> <br />. <br /> <br />o <br />o <br /> <br />20 <br /> <br />40 <br /> <br />60 <br /> <br />80 <br /> <br />100 <br /> <br />Volts <br /> <br />FIG. 1 The effect of alternating current electronarcosis at 3 dif- <br />ferent potentials on mean narcosis time (:!: SE) <br /> <br />200 <br /> <br />OJ <br />-g 150 <br />o <br />3l <br /> <br />f <br /> <br />f <br /> <br />.S <br />] 100 <br />"' <br />'w <br />o <br />~ <br />~ 50 <br /> <br />f <br /> <br />o <br />o <br /> <br />10 20 <br />Temperature .C <br /> <br />FIG. 2 The effect of 100 Vp rectified current electron~rc,?5is at 3 <br />different water temperatures on mean narcosIs time (:!: <br />SE) <br /> <br />30 <br /> <br />215 <br /> <br />f-t <br />I <br /> <br />f <br />f <br />f <br />f <br />, <br />: <br />t <br />k <br />k <br />! <br />I <br />I <br />! <br />i' <br />, <br />. <br />1 <br />c'. <br />c <br /> <br />I <br />