Essential oils from Citrus x aurantium and Citrus x latifolia (Rutaceae) have anesthetic activity and are effective in reducing ion loss in silver catfish ( Rhamdia quelen )

ABSTRACT This study investigated the anesthetic effect of the essential oils (EOs) from the peel of Citrus x aurantium (EOCA) and Citrus x latifolia (EOCL) on silver catfish Rhamdia quelen. Fish were exposed to different concentrations of EOCA and EOCL to determine time of anesthesia induction and recovery. Induction of anesthesia was observed in all fish exposed to 400, 600 or 800 μL L−1 EOCA and 300, 400 or 500 μL L−1 EOCL. Another group of fish were exposed for 8 h to 50, 100, or 200 μL L−1 of either EOs. Overall, fish exposed to ethanol and both EOs presented higher ventilatory frequencies (VF) than the control group throughout the 8 h of exposure. Net ion (Na+, K+ and Cl−) effluxes and ammonia excretion were significantly lower in fish exposed to 50, 100 or 200 μL L−1 of either EOs compared to control fish. Mortality was 37% in fish exposed to 200 μL L−1 of either EOs after 8 h. These findings suggest that EOCA and EOCL are useful anesthetics and sedatives for Rhamdia quelen, but their usefulness as alternatives to reduce stress in fish transportation at the lower concentrations tested (50-100 µL L−1) deserves further study.

摘要 本研究探讨了苦橙（Citrus x aurantium，EOCA）与墨西哥莱檬（Citrus x latifolia，EOCL）果皮精油（essential oils, EOs）对银鲶（Rhamdia quelen）的麻醉效果。研究通过设置不同浓度的EOCA与EOCL处理组，测定受试银鲶的麻醉诱导时长与恢复时长。在暴露于400、600或800 μL·L⁻¹ EOCA，以及300、400或500 μL·L⁻¹ EOCL的组别中，所有受试银鲶均成功实现麻醉诱导。另有一组受试银鲶分别暴露于50、100或200 μL·L⁻¹的任意一种精油中，暴露时长为8小时。整体而言，在8小时暴露周期内，乙醇处理组与两种精油处理组的受试银鲶呼吸频率（ventilatory frequencies, VF）均显著高于对照组。与对照组相比，暴露于50、100或200 μL·L⁻¹任意一种精油的受试银鲶，其净离子（Na⁺、K⁺与Cl⁻）外流速率与氨排泄量均显著降低。暴露于200 μL·L⁻¹任意一种精油的受试银鲶，在8小时暴露后死亡率达37%。本研究结果表明，EOCA与EOCL可作为银鲶的有效麻醉剂与镇静剂，但在本次试验的低浓度（50~100 μL·L⁻¹）下，其作为缓解鱼类运输应激替代方案的应用价值仍需进一步探究。