Evaluation of the sedative and anaesthetic effects of five different concentrations of alfaxalone in goldfish, Carassius auratus

• Alfaxalone solubilised in beta cyclodextrin is tested as an anaesthetic in goldfish.
• 0.5 mg alfaxalone/L water was sufficient to induce sedation within 37 ± 7 min.
• 2 mg alfaxalone/L water was sufficient to induce sedation within 7 ± 1 min.
• 5 mg alfaxalone/L water was sufficient to induce anaesthesia within 28 ± 8 min.
• 7.5 mg alfaxalone/L water was sufficient to induce anaesthesia within 14 ± 2 min.

Anecdotal publications describe induction of anaesthesia in fish with alfaxalone. This study's objective was to determine the water concentrations of alfaxalone required to sedate and anaesthetise goldfish. The study was conducted as an unmasked, parallel design, randomised trial with five groups each of six healthy goldfish, Carassius auratus. Fish with a mean length (± SD) of 8.5 (± 2.5) cm were immersed in individual water tank with controlled temperature (23–25 °C), pH (6.8–7.2) and osmolality (38–45 mOsm/L), at concentrations of 0.15, 0.5, 2.0, 5.0 and 7.5 mg alfaxalone per litre, complexed with hydroxypropyl-beta cyclodextrin. Monitoring of fish included body approach reaction, maintenance of equilibrium, operculum movement and response to noxious stimuli. Depth of anaesthesia was determined using a modified published scale. A concentration of 0.15 mg alfaxalone/L water was insufficient to induce sedation or anaesthesia. Mean sedation induction time ± SD (range) after immersion at concentrations of 0.5 and 2.0 mg alfaxalone/L were 37 ± 7 (34–50) min and 7 ± 1 (5–8) min respectively. Anaesthesia was not achieved at those concentrations. After immersion in water containing 5.0 and 7.5 mg alfaxalone/L mean sedation induction times were 4 ± 2 (2–6) min and 2 ± 1 (1–2) min respectively, mean anaesthesia induction times were 28 ± 8 (16–35) min and 14 ± 2 (12–18) min respectively and mean full recovery times were 32 ± 18 (20–67) min and 36 ± 13 (23–53) min respectively. No adverse events were seen. The lowest water concentrations of alfaxalone identified to induce sedation and anaesthesia in goldfish (C. auratus) were 0.5 mg/L and 5 mg/L respectively.