Nearly all cephalopods such as squid, octopuses and cuttlefish can squirt ink as an escape mechanism when threatened. Not unlike a magician throwing a smoke bomb, these animals are able to create dark, thick clouds of pigment in the water, masking their quick retreat. This ability is possible through the use of the squid's ink sacs and water propulsion.
Biological Ink Well
Cephalopods that squirt ink have a muscular "bag" in their bodies located underneath the gut and connected to the anus. This modified gland is called an ink sac, and contains mostly pure melanin -- the same pigment that colors our skin -- mixed with tyrosinase, an enzyme that impairs the senses of smell and taste. The ink also contains trace elements of dopamine and L-DOPA. These neurotransmitters may possibly warn other cephalopods about the threat of enemies.
The anus excretes just below the mantle, or what looks like the head of the squid or octopus. The mantle contains the stomach and the mantle cavity, an empty space that fills with water. By quickly squeezing the water from the cavity, the cephalopod creates a kind of jet propulsion that pushes the squid, octopus or cuttlefish forward.
When a squid inks, it expels pigment from the ink sac that opens into the anus. This mixes with the jet of water pushed from the mantle. It happens quickly and ink immediately clouds the surrounding water.
Which Way Did He Go, George?
Ink squirted straight from the mantle acts as a smokescreen, giving the octopus or squid time to escape. Confused predators have difficulty tracking the cephalopod's path and may give up the chase.
Often while inking, the squid or octopus will change to a darker color, mimicking its own cloud of ink that now appears to be drifting away.
Ever the magician, the cephalopod, when threatened, sometimes combines mucus from its body with the ink. This seems to give the ink more solid form, further confusing an enemy by resembling the body of the squid or octopus. The predator will attack the fake prey, while the cunning cephalopod makes a hasty exit. Like any good illusionist, he doesn't want to stick around while his audience figures out the trick.
Aw, You Made Me Ink
Caring for a pet cuttlefish, squid or octopus does include situations where the animal may become stressed and ink. Inking presents a number of problems, including physical damage to your pet. Because inking uses a blast of water, this propulsion can speed your squid or octopus smack into the end of the tank, injuring them.
The ink itself is not toxic, but it can end up coating your pet's gills. With a closed container and no opportunity to escape the cloud, a buildup of ink can suffocate the octopus or squid.
If your pet squid or octopus inks in the aquarium, immediately remove the suspected cause of stress. Siphon the ink from the tank, change the water, and use a protein skimmer to ensure removal of any trace pigment. If your aquarium filter uses carbon, replace the carbon after an inking incident, as it will be ruined.
If your pet squid, octopus or cuttlefish is well cared for in his aquarium, and kept free from stimuli that might make him ink, his life expectancy is six months to two years.