Anaesthetic Potential of Propofol for Nile Tilapia (Oreochromis niloticus): Effect of Anaesthetic Concentration and Body Weight

Handling or transporting fish can strongly affect physiology and behaviour, and anaesthesia is often used to minimize stress or injuries. The potential of propofol as an immersion anaesthetic for Nile tilapia (Oreochromis niloticus) was investigated in this study. Nile tilapia were divided into groups based on a body mass criteria of 10, 50, 100, 150 and 200 g, and subjected to different propofol concentrations (2.5, 5, 7.5, 10 or 12.5 mg L⁻¹) using 3 individuals per size class for each prepared anaesthetic solution. Fish were placed in the prepared anaesthetic baths and times to lose reflex to mild touch as well as induction of full immobilisation recorded. Behavioural markers such as loss of the righting reflex and respiratory responses were also monitored. Following the induction of full anaesthesia, blood samples were drawn from each of the 200 g fish for haematological analysis. Induction times for deep anaesthesia (Stage IV) decreased significantly (p < 0.05) with increasing propofol concentrations for all size classes and increased as a function of increasing fish size. Recovery from anaesthesia was smooth in all size classes and exposure to higher doses of anaesthesia resulted in a general trend of prolonged recovery times. Larger fish showed a general trend of faster recovery times than smaller fish under the different propofol concentrations. Besides reporting the practicality of propofol as an immersion anaesthetic, this study has also demonstrated the importance of considering size when anaesthetizing Nile tilapia with propofol.