Anesthetic Efficacy of Magnesium Chloride and Ethyl Alcohol in Temperate Octopus and Cuttlefish Species

Cephalopods are important in biologic and biomedical research, yet relatively little objective information is available to guide researchers and veterinarians regarding the best methods for anesthetizing these animals for various experimental procedures. Recent studies demonstrate that ethyl alcohol and magnesium chloride are effective at depressing efferent and afferent neural signals in some tropical cephalopod species when measured via the pallial nerve. Here we used similar methods to test 2 temperate species (Octopus bimaculoides and Sepia officinalis) and demonstrate that (1) ethyl alcohol and magnesium chloride were effective at reversibly depressing evoked activity in the pallial nerve, (2) ethyl alcohol generally had shorter induction and recovery times compared with magnesium chloride, (3) both agents were associated with a latency between the behavioral and neural effects, and it was longer with magnesium chloride, and (4) senescent animals generally had longer induction or recovery times than young animals. Both agents successfully anesthetized both life stages; however, our data show that assessing anesthesia based solely on behavior may lead to premature commencement of invasive procedures. We conclude that temperate cephalopods can be humanely, effectively, and completely anesthetized by using these 2 agents and that the loss of neural signal we show here is consistent with true anesthesia and not merely paralysis. This relatively simple, nondestructive nerve recording technique can be applied to the study of other prospective anesthetic agents in cephalopods.