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458 J. A. MADDEN AND A. H. HOUSTON <br />Horgan, 1968), and may be causally related to the persistent variations in water- <br />electrolyte status typically observed in specimens during recovery. Finally, although <br />tricaine methane sulphonate is rapidly cleared from the blood (Houston & Woods, <br />1972) significant tissue residues are found for several hours Q. B. Hunn, personal <br />communication). <br />Observations of this type suggest the desirability of considering possible <br />alternatives to chemical anaesthesia. Electroshock has been widely used in <br />field studies, but only rarely as an anaesthetic tool (Field, Elvejem & Juday, 1943; <br />W. Beamish, personal communication). This study was undertaken to explore the <br />use of electroanaesthesia with freshwater fishes and has emphasized the immediate <br />and longer term effects of electroanaesthesia on selected haematological and body <br />chemistry parameters in rainbow trout, Salmo gairdneri. <br />II. MATERIALS AND METHODS <br />Origin and maintenance of stocks <br />Two year old trout of both sexes ranging in weight from 90 to 100 g were purchased from <br />a local commercial hatchery, and were maintained under conditions comparable to those <br />described by Houston et al., 1971a. As evidenced by general activity, feeding behaviour and <br />the absence of obvious disease symptoms, the stock was judged to represent a healthy popula- <br />tion. <br />Experimental protocol <br />Three groups of animals were used in the investigation. That designated as the control <br />group, consisted of animals netted from acclimation tanks (10° C), stunned and sampled <br />as quickly as possible. A second group included animals subjected to electroanaesthesia <br />and immediately sampled. Finally, the post-treatment or recovery group consisted of <br />animals which were electroanaesthetized and sampled after 3, 6, 12 and 24 h periods of <br />recovery. ,, <br />E7ectroanaesthesia <br />Specimens were transferred individually to 101 baths containing 0.1 % NaCl in acclimation <br />tank water. An immersible bipolar probe was used to induce the electroanaesthesia. Pre- <br />liminary trials indicated that a 30 sec discharge of 110-volt a.c. current at 350 mA was <br />adequate for specimens of the size used. <br />Analytical procedures <br />The consequences of electroanaesthesia were assessed by reference to blood haemoglobin <br />and haematocrit, plasma glucose, and plasma and tissue levels of sodium, potassium, calcium, <br />magnesium, and chloride as well as tissue water content. Tissue water distribution was <br />estimated by reference to the chloride space approximations of extra-cellular phase volume. <br />Blood samples were drawn by caudal puncture into ammonium heparinized syringes. <br />Haematocrit and haemoglobin were measured immediately and plasma glucose and chloride <br />as quickly as possible after centrifugation. The remaining plasma was then frozen (-12° C) <br />for subsequent cation analyses. Muscle samples were taken from the epaxial muscle mass, <br />weighed, dried to constant weight (60° C, 96 h) and frozen in individual sample containers <br />prior to analysis. <br />Analytical techniques were, with one exception, comparable to those used in earlier studies <br />in this series (Houston et al., 1971a). Tissue samples for cation analyses were sonicated and <br />extracted in aqueous 5% trichloracetic acid-lanthanum hydrochloride before dilution and <br />atomic absorption analysis. This procedural modification reduced tissue preparation time <br />without concomitant reduction in analytical precision. <br />PHYSIOLOGICAL CHANGES WITH ELECTROANAESTHESIA 459 <br />M. RESULTS AND DISCUSSION <br />Overt effects of electroanaesthesia <br />Current discharge was followed by operculum flaring, arching of the body, skin blanch- <br />ing and the cessation of swimming movements and, as determined by polygraphic <br />recording, cardiac and respiratory activity. Most of the fish floated momen- <br />tarily on back or side before sinking to the bottom of the tank. Unco-ordinated super- <br />ficial' twitching' or ` shivering' was usually observed from 1 to 2 min after discharge <br />ceased. Ventilation and cardiac activity were spontaneously resumed within 2 to <br />4 min. After 10 min colour patterns appeared normal. Most specimens were unres- <br />ponsive to mechanical stimuli for about 20 min. Inasmuch as the time required for <br />implantation of electrocardiograph electrodes and dorsal aortic buccal and cleithral <br />and urinary bladder catheters averages 17±1 min in trout (Houston et al., 1973) this <br />period of anaesthesia appears adequate for most procedures. Equilibrium was <br />usually regained after 30 min and swimming movements commenced after a further <br />10 to 20 min. As judged by equilibrium, swimming and spontaneous activity, most <br />specimens appeared to have recovered after an hour. <br />Of 80 fish tested in this phase of the study, three died within 24 h. This mortality <br />rate compares reasonably with that encountered with many chemical anaesthetics. <br />Dissection revealed rupture of one or more vertebrae at the base of the skull coupled <br />with extensive haemorrhage. Presumably this was the result of excessive body wall <br />muscle contraction. <br />Modifications in haematology and body chemistry <br />Results obtained in the study are summarized in Table I. <br />Immediate effects of electroanaesthesia <br />Inasmuch as handling was comparable in groups one and two, the initial effects <br />of electroanaestbesia can be ascertained by their comparison. There was little evi- <br />dence of any significant change in several parameters including haemoglobin, plasma <br />calcium and magnesium and tissue sodium, magnesium and water content. Several <br />other values declined to some greater-or-lesser extent; mean haematocrit by about <br />8% from 36.0±1.0 to 33.1±1.2%, tissue chloride by approximately 29% from <br />14.3±1.1 to 102±1.2mequiv/kg and chloride space by roughly 39% from 99±22 <br />ml/kg to 60±10 ml/kg. The largest proportional decrease was seen in the plasma <br />potassium level which fell from 3.7±0.5 to 1.8±0.4 mequiv/1. All other parameters <br />showed some increase in magnitude with the most marked effects being observed <br />for plasma glucose (56.5±3.5 to 83.5±6.9 mg/100 ml+48%) and tissue calcium <br />(4.6±0.9 to 7.5±2.2 mequiv/kg+60%). <br />These variations can be loosely compared with those obtained earlier for the <br />immediate consequences of exposing the related brook trout to tricaine methane <br />sulphonate (Houston et al., 1971a). Several differences in effect can be noted. Whereas <br />electroanaesthesia seemingly prompted little change in either haemoglobin or haemato- <br />crit, chemical anaesthetization has been shown to result in a marked haemoconcen- <br />tration. Plasma glucose elevation was observed in both cases but was pronounced <br />in electroanaesthetized fish. Similarly, chloride increased in electroanaesthetized <br />fishes exceeding the minimal changes seen in chemically anaesthetized specimens. <br />Qualitatively similar variations were observed with respect to potassium which de- <br />clined in concentration and sodium which increased in concentration. Neither calcium