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
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