Abstract
This study aimed to explore different substances (or cold sea water) as potential anesthetic agents to facilitate short-term handling in Octopus maya juveniles. We investigated oxygen consumption before (baseline), during (first 600 s of exposure) and after anesthesia (recovery) of octopuses (n = 98; 1.67 ± 0.5 g) exposed to cold sea water (SW; 11 and 13°C), ethanol (EtOH; 0.5; 1.5 and 3.0%), magnesium chloride (MgCl2; 0.75; 1.5 and 3.75%), ethanol combined with magnesium chloride (Mix; 1.5:0.75%; 0.75:1.13%; and 2.25:0.37%) and clove oil (0.15 mL L–1). After exposure, the animals were handled for 180 s (exposed to air) and weighted. Two experimental groups not exposed to anesthetics (with or without handling) were also evaluated. The criteria for general anesthesia were analysed. Times of induction and recovery, incidence of attack response after recovery and possible longer-term effects of repeated general anesthesia on growth and mortality of the octopuses were evaluated. During anesthesia, O. maya juveniles exposed to SW (11 and 13°C), EtOH (0.5; 1.5 and 3.0%), Mix (0.75:1.13%), and clove oil, presented a significant decrease on oxygen consumption. In animals exposed to different concentrations of EtOH and Mix 0.75:1.13%, this decrease was registered after an increase on oxygen consumption. Animals exposed to MgCl2 did not show significant changes on oxygen consumption, except for animals exposed MgCl2 3.75%, which showed a significant increase on oxygen consumption. At the end of recovery, except for octopuses exposed to clove oil and MgCl2 0.75%, the values of oxygen consumption observed were comparable to the ones registered during baseline. Animals exposed to SW 11°C, EtOH 3.0%, Mix 1.5:0.75% and MgCl2 3.75% fulfilled the criteria defined for general anesthesia. Exposure to MgCl2 (all concentrations), SW 13°C and clove oil reduced or inhibited the incidence of attack response after recovery. Except for animals exposed to clove oil, growth of the juveniles was not affected by the exposure to the different substances. Short-term handling (180 s) of O. maya juveniles can eventually be carried out without anesthesia. However, to facilitated handling, we suggest the use of EtOH 3.0% or cold sea water 11°C.
Highlights
General anesthesia may be defined as a controllable and reversible state, which includes loss of consciousness, analgesia, suppression of reflex activity, and muscle relaxation (Flecknell, 2015)
During exposure to the presumed anesthetic agents, the results on oxygen consumption showed that the metabolic rate was affected by treatment and time of exposure (Table 2)
In octopuses exposed to both temperatures of cold sea water (11 and 13◦C), a significant decrease on oxygen consumption was recorded after 120 s of exposure, producing non detectable values of metabolic rate (p < 0.00001) (Figure 2B)
Summary
General anesthesia may be defined as a controllable and reversible state, which includes loss of consciousness, analgesia, suppression of reflex activity, and muscle relaxation (Flecknell, 2015). With few exceptions (Andrews and Tansey, 1981; Pugliese et al, 2016; Butler-Struben et al, 2018) the majority of anesthetic studies in cephalopods do not explore in-depth the efficacy of the commonly used agents and the physiological effects of anesthesia on the animals. Another limitation is the lack of standardized anesthesia protocols for cephalopods, since distinct methods are described in the literature
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