How to Knock Out an Octopus

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Octopuses, as if anyone had to remind you, are amazing animals. They can squeeze into tiny spaces, break into locked boxes, recognize and remember people, and cover their tracks after pulling off a daring crayfish theft. More and more, says naturalist Sy Montgomery, the  scientists who study octopuses are “convinced that these boneless, alien animals … have developed intelligence, emotions, and individual personalities.” 

Legislators are coming around to that conclusion, too, and laws in the United Kingdom, European Union and Australia mandate that cephalopods used in research be treated humanely. In some cases, this means anesthetizing them so they don’t experience pain or distress during transport or experiments. That presents scientists with a problem: how do you put an octopus under?

Many researchers agree that octopuses feel pain based on the complexity of their nervous systems and the fact that they’ll respond to painful stimuli, but how they experience it and whether it’s similar to the way vertebrates do is anything but clear. And if we’re not sure how the animals experience pain, preventing it from happening is pretty tricky. “While we’re pretty adept at anesthetizing mice and monkeys, the mollusk body works so differently that human researchers are still largely in the dark,” says Katherine Harmon Courage, author of Octopus! The Most Mysterious Creature In the Sea. 

Now a trio of biologists from Italy and the UK have shone at least a little light on the problem. Past attempts at anesthetizing cephalopods using things like muscle relaxants, ethanol, benzocaine, clove oil, and very cold water often did more harm than good. In some cases the animals were simply paralyzed instead of anesthetized, while other times there was only a local anesthetic affect. At least a few unlucky squid were killed during attempts to put them under. Gianluca Polese, William Winlow, and Anna Di Cosmo decided to try a different approach and tested isoflurane, an inhalational anesthetic used in human and veterinary medicine, on the common octopus (Octopus vulgaris).

They bought 16 octopuses at a fish market in Naples and brought them back to their lab, where they pumped vaporized isoflurane into the animals’ tanks. As the isoflurane concentration crept up to 2 percent, the octopuses stopped responding to being touched and showed no protective reflexes. Meanwhile, their skin color changed to almost white, except for a few random flashes. An octopus’ color and patterns are under direct control of the brain, so the paling and haphazard flashes are signs that normal motor coordination is lost. After just 10 minutes of immerison in 2 percent isoflurane, the researchers concluded, “the animals were clearly relaxed, unresponsive, and anesthetized.” And all of the animals, except for two who died after exposure to a higher dose of the anesthetic, recovered quickly and resumed normal behavior after an hour in fresh seawater.

The researchers captured some of the process on video, which you can see at the American Association for the Advancement of Science’s website.