Comparative effects of clove bud powder ( Syzygium aromaticum ) and sodium bicarbonate on anaesthetic induction and recovery in juvenile three-spotted tilapia ( Oreochromis andersonii , Castelnau 1861)

Access to affordable and effective anaesthetic agents is crucial for the welfare of cultured fish, particularly in resource-limited settings. This study evaluated clove bud powder (Syzygium aromaticum) and sodium bicarbonate as cost-effective anaesthetics for juvenile Oreochromis andersonii, a resilient and locally preferred species widely used in Southern African polyculture systems. Juveniles (8–10 weeks old; mean weight 18 ± 0.5 g; mean length 102.1 ± 7.0 mm) were obtained from the concrete experimental ponds of the Genetic Improvement Programme at NARDC, acclimated for two days under controlled temperature and continuous aeration, and immersed in clove powder (1–4 g/L) or sodium bicarbonate (5–40 g/L) solutions in triplicate 20-L tanks. Anaesthesia was assessed across three standardised stages, with Stage III defined as loss of equilibrium and reduced continuous opercular movements. Induction time decreased with increasing concentrations of both agents, while recovery time generally increased, except between 5 and 10 g/L sodium bicarbonate. Based on rapid induction, safe recovery, and behavioural responses, optimal concentrations were identified as 2 g/L for clove bud powder and 30 g/L for sodium bicarbonate. These findings demonstrate that both agents are effective, with sodium bicarbonate offering a rapid, safe and cost-effective option for routine hatchery procedures.