Assessment of Various Anesthetic Agents on Octopus vulgaris Paralarvae

European Directive 2010/63 addresses the welfare of cephalopod species used in scientific projects under European jurisdiction and covers experimental procedures likely to cause pain, suffering, distress, or lasting harm. These procedures require authorization from the National Competent Authorities. In aquaculture research, some procedures require the temporary immobilization of individuals to allow for measuring body parameters (i.e., weight, sex, gonad condition, and others), avoiding any damage. This study compares three anesthetics used on common octopus, Octopus vulgaris, paralarvae to reach a state of sedation. The anesthetics were tested for their effects at different concentrations: magnesium chloride (6.8, 13.6, 20.4, and 27.4 g/L), ethanol (8, 10, and 12 mL/L), and clove oil (0.2, 0.3, and 0.4 g/L). Three variables were monitored: induction, recovery, and stressful behavior of paralarvae during treatments. Significant differences were found between anesthetics, both in the induction and recovery time, and between concentrations of the same anesthetic. The shortest times of induction and recovery corresponded to ethanol at low concentrations, 10 mL/L (20±1 sec) and 8 mL/L (19±2 sec), respectively. Clove oil at 0.2 g/L was the slowest to reach sedation (340±7 sec). Magnesium chloride at 20.4 g/L showed longer recovery times (554±201 sec) with increasing concentrations. Octopus paralarvae showed adverse behavior only under clove oil treatments, whose use is therefore considered inadmissible. This study shows that ethanol at 10 mL/L may be suitable as a reliable anesthetic for octopus paralarvae, diminishing the induction and recovery time without showing any stressful behavior.

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