Cardiac response of tambaqui Colossoma macropomum anaesthetised with geraniol and citronellol

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Electrocardiographic recordings (ECG) provide information on the duration of the action potential and the heart rhythm. Altered ECG may reflect important disturbances to the cardiac function. The aim of this study was to evaluate putative cardiotoxic effects in Colossoma macropomum upon exposure to geraniol (GRL – 70 μL L−1) and citronellol (CTL – 90 μL L−1) in anaesthetics baths. The fish were randomly distributed across the following treatments: a) control (basal recordings), b) vehicle control (ethanol), c) fish exposed to GRL – 70 μL L−1 and subsequent recovery, and d) fish exposed to CTL – 90 μL L−1 and subsequent recovery, and e) washout from ethanol. Five-minute duration recordings were used. The parameters heart rate (HR) (beats min−1), QRS complex amplitude (mV), R-R interval (s) (time between two successive QRS complexes), Q-T interval (s) (ventricular contraction) and QRS duration (s) (ventricular depolarization) were investigated. No mortality was observed and all animals recovered post exposure. The controls and ethanol-exposed fish presented normal patterns in ECG tracings showing sinus rhythm. Some alterations were observed during induction, e.g., a negative chronotropic effect was observed in fish exposed to GRL, however, with maintenance of the sinus rhythm. Only the Q-T interval was longer than that of the controls. On the other hand, during induction with CTL, marked bradycardia with arrhythmia and prolongation of the Q-T and R-R intervals and QRS complex duration were observed, indicating a potential for atrioventricular blockade. During recovery, albeit slow, all parameters were gradually returning to sinus rhythm, suggesting that although important cardiac changes occurred during induction, mostly with CTL, they did not affect survival. In conclusion, both products induced anaesthesia with full body immobilisation and provoked some cardiac alterations, however, while GRL allowed for a faster recovery, CTL seemed to require a more prolonged time for full resumption of the normal cardiac function.