Jambu, Spilanthes acmella as a novel anaesthetic for juvenile tambaqui, Colossoma macropomum: Secondary stress responses during recovery

• This is the first report of jambu extract being used as an anaesthetic for fish.
• All concentrations tested (5–25 mg L−1) induced deep anaesthesia and uneventful recovery in juvenile tambaqui.
• Only transient physiological changes were observed in blood during recovery.

The aim of this study was to evaluate the efficacy of the waxy extract of jambu flowers, Spilanthes acmella as an anaesthetic for fish, using juvenile tambaqui Colossoma macropomum as a model. The times to induction and recovery after short-term anaesthesia were evaluated by concentration-response trials and secondary stress responses. Juveniles were placed in aquaria containing five different concentrations of jambu extract (5, 10, 15, 20, 25 mg L−1) and the times of anaesthetic induction and recovery were determined. Sham control fish and fish exposed to ethanol-added water were used as controls. The secondary stress responses of fish following anaesthesia with jambu extract (20 mg L− 1) were investigated through an assessment of whole blood variables: glucose, ions (Na+, K+, and Ca++), osmolality, haematocrit (Htc), haemoglobin (Hb), partial pressures of CO2 (pCO2) and O2 (pO2), bicarbonate concentration (HCO3−), and pH. Deep anaesthesia was observed at all concentrations tested in this study. The use of 20 mg L− 1 of this extract is recommended for rapid induction (< 3 min) and uneventful recovery (< 5 min) from deep anaesthesia; while the concentration of 2 mg L− 1 is sufficient to promote sedation. Only transient changes in secondary stress responses were observed in tambaqui during recovery, with most parameters returning to initial values within 48 h post-anaesthesia. Therefore, the extract of jambu flowers may be considered an efficient anaesthetic for tambaqui and other fish species.Statement of relevanceThis is the first study using extract of Jambu, Spilanthes acmella as an anaesthetic for aquatic organisms.