Cardiac response in tambaqui Colossoma macropomum anaesthetised with Piper divaricatum essential oil

The aim of this study was to evaluate the electrocardiographic responses of Colossoma macropomum exposed to short-term baths using the essential oil of Piper divaricatum (EOPD) as an anaesthetic-like agent in different doses (40, 60, and 80 μL L^-1). Cardiac responses throughout and after exposure to EOPD were monitored and evaluated through mean heart rate (HR), duration and amplitude of the QRS complex (ventricular depolarization), and Q-T (ventricular contraction) and R-R (time between two successive QRS complexes) wave intervals. Across all doses, there was a marked depression of the HR, mainly at 80 μL L^-1 EOPD. Mean amplitudes recorded for the QRS complex and Q-T interval at 40 μL L^-1 EOPD were indistinguishable from the control, which could reinforce this concentration as sufficient and safe to promote fast anaesthesia without affecting cardiac function. Recovery from bradycardia, duration of the R-R interval, and QRS complex were similar at 60 and 80 μL L^-1 EOPD; however, the Q-T interval at 80 μL L^-1 EOPD revealed a more pronounced cardiac depression in relation to the controls and fish exposed to 60 μL L^-1 EOPD. Thus, we conclude that 40 μL L^-1 EOPD should suffice to induce fast, deep, and safe anaesthesia in tambaqui juveniles, whereas the concentration of 80 μL L^-1 led to a greater depression of the cardiac function, albeit showing effect reversibility.