Propofol and essential oil of Nepeta cataria induce anaesthesia and marked myorelaxation in tambaqui Colossoma macropomum: Implications on cardiorespiratory responses

This study aimed at characterizing the modulation of skeletal muscle contraction and cardiorespiratory response of tambaqui, Colossoma macropomum submitted to baths using anaesthetic concentrations (capable of inducing fast, i.e. < 5 min, and full body immobilization) of propofol (PRP) and essential oil of Nepeta cataria (EON). For the evaluation of electromyography, electrocardiographic data, and opercular beat intensity (OBI) and rate (OBR), fish (5.6 ± 1.8 g, 8.0 ± 0.3 cm, total length) were assigned to the following groups: a) control (basal recording), b) ethanol-exposed fish (vehicle control), c) fish submitted to induction with EON at 175 μL L−1 and subsequent recovery, and d) fish submitted to induction with PRP at 4 μL L−1 and subsequent recovery. Eight fish (n = 8) per group were used. Both products induced full body immobilization and suppressed (99.9%) dorsal muscle contraction power, determining a general anaesthesia-like state. During exposure to either anaesthetic, cardiac function was transiently affected, with decreased heart rates (42-43%) and a mild arrhythmia in PRP recovering fish. Moreover, ventilatory capacity was reduced with this drug (85.3% and 59.6% decrease in OBI and OBR, respectively), yet without mortality. On the other hand, EON did not alter ECG tracings, allowing for the maintenance of normal ventilation intensity during exposure, albeit a slight increment in OBR occurred during deep anaesthesia. This study confirms propofol anaesthesia in fish and presents N. cataria essential oil as a novel and safe natural anaesthetic for juvenile Colossoma macropomum and potentially for other teleost species.