Effects of water temperature and body weight on anaesthetic efficiency in marbled rabbitfish (Siganus rivulatus)

The effects of four anaesthetic agents, tricaine methanesulphonate (MS‐222) (112.5 mg L^?1), 2‐phenoxyethanol (400 μL L^?1), clove oil (70 mg L^?1) and benzocaine (65 mg L^?1) on juvenile marbled spinefoot (Siganus rivulatus) of three mean body weights (7.3 g, 19.1 g, 55.5 g) and at three temperatures (20, 25, 30°C) were evaluated. In addition, the relationship between body lipid content and efficacy of the four anaesthetic agents was evaluated in juvenile S. rivulatus. Times necessary for induction and recovery were recorded. Significant effects of temperature on induction and recovery times were observed. Induction and recovery times decreased with increasing water temperature. No uniform relationship between body weight of juvenile marbled spinefoot and anaesthetic efficacy was observed. Body fat content was positively correlated with induction time only when MS‐222 was used but did not affect induction times of fish exposed to 2‐phenoxyethanol, clove oil or benzocaine. Recovery times were generally longer for all fish containing more body fat. Results of the study show that anaesthetic efficiency increases with increasing water temperature but is not strongly affected by body weight for juvenile marbled spinefoot. In addition, body fat in fish affected the efficacy of the various anaesthetic agents tested in this study, generally slowing down recovery.