Anaesthetic efficacy of eugenol on iridescent shark, Pangasius hypophthalmus (Sauvage, 1878) in different size classes

摘要

Anaesthetic efficacy of eugenol was investigated on iridescent shark, Pangasius hypophthalmus. Fish (2, 5, 10 and 20g) subjected to 20-200mg L-1 eugenol and behavioural response as well as induction and recovery times were recorded. Induction and recovery times were significantly affected by eugenol concentration as well as fish weight (P0.05). Generally, 27-300s after exposure to 20-200mg L-1 eugenol, iridescent sharks reached stage 3 anaesthesia (suitable for general handling). Fish entered stage 4 anaesthesia (suitable for surgery and blood sampling) over 54-710s exposure to such concentrations. Recovery time was 109-600s in all weight classes as well as eugenol concentrations. Mortality (44-100%) was only observed in 2g fish when subjected to 110-170mg L-1 eugenol. This study, for the first time, showed behavioural response of iridescent shark to anaesthesia as well as effectiveness of eugenol as anaesthetic in this important aquaculture-ornamental species. According to the models obtained in this study, minimum eugenol concentrations to induce anaesthesia over less than 3min were 53.8-81.5mg L-1 in 2-20g fish. Likewise, maximum eugenol concentrations in which fish recovered over less than 5min were 65.9-105.8mg L-1 in 2-20g fish.