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). 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 EOPD. Mean amplitudes recorded for the QRS complex and Q-T interval at 40 μL L 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 EOPD; however, the Q-T interval at 80 μL L EOPD revealed a more pronounced cardiac depression in relation to the controls and fish exposed to 60 μL L EOPD. Thus, we conclude that 40 μL L EOPD should suffice to induce fast, deep, and safe anaesthesia in tambaqui juveniles, whereas the concentration of 80 μL L led to a greater depression of the cardiac function, albeit showing effect reversibility.