Essential oil of Piper divaricatum induces a general anaesthesia-like state and loss of skeletal muscle tonus in juvenile tambaqui, Colossoma macropomum

Abstract

This study investigated the anaesthetic potential of the essential oil from the leaves of Piper divaricatum (EOPD) through evaluation of the behaviour and electromyographic (EMG) recordings from the fish Colossoma macropomum which was used as an animal model. Initially, fish (3.9 ± 0.3 g; 6.4 ± 0.49 cm, total length) were subjected to short-term anaesthetic baths in five different concentrations of the EOPD: 25, 30, 35, 40 and 45 μL.L−1 to record the latencies for deep anaesthesia and recovery. Ten fish per concentration were used (n = 10) and each animal was considered a replicate and used only once. Thereafter, for the evaluation of EMG, fish (5.6 ± 1.8 g; 8.7 ± 0.52 cm, total length) were assigned to the following groups: a) sham control (basal recordings) and b) fish exposed to the EOPD at 40 μL.L−1 and subsequent recovery in anaesthetic-free water. Nine fish per analysis (n = 9) were used. The EOPD presented a high concentration of methyleugenol (71.36%) and prompted immediate behavioural changes in fish. Initially, hyperactivity was observed, followed by loss of the righting reflex and full body immobilization. All concentrations tested were capable to promote an anaesthetic-like state in tambaqui, with 40 μL.L−1 being the minimal concentration necessary to induce a rapid immobilization, i.e. < 3 min. The EMG showed a marked and reversible myorelaxation effect, confirming this oil as an indisputable muscle relaxant agent. The EOPD was capable of promoting a general anaesthesia-like state, with complete body immobilization of Colossoma macropomum at all concentrations tested. Gradual increases in frequency and amplitude of EMG tracings confirm the reversibility and uneventful resumption of normal swimming behaviour observed during recovery. Our results underscore the anaesthetic potential and myorelaxant effects of Piper divaricatum essential oil.