Cephalopod ink

Cephalopod ink is a dark or glowing liquid that most species of cephalopods release to escape danger. Cephalopods include animals like squid, octopuses, and cuttlefish. Almost all of them can use ink to confuse predators, except for the Nautilidae and the Cirrina, which are deep-sea octopuses that do not use ink.

The ink comes from special ink sacs found between the gills of the cephalopod. When it is released, a jet of water from the siphon helps spread the ink wider in the water. The ink is dark because of a substance called melanin. Different cephalopods make inks of slightly different colours—octopuses usually have black ink, squid have blue-black ink, and cuttlefish have a shade of brown.

Some other sea creatures, like sea hares, also use a similar trick to defend themselves.

Properties and chemistry

Cephalopod ink is made of different chemicals, depending on the type of cephalopod. The main parts of the ink are melanin and mucus. It may also contain tyrosinase, dopamine, and L-DOPA, along with small amounts of free amino acids such as taurine, aspartic acid, glutamic acid, alanine, and lysine.

Ink helps protect cephalopods from being caught by fish. It confuses the fish both by looking dark and by using chemicals. Some fish, like moray eels, can sense chemicals well, and ink may irritate or confuse them. Ink can also warn other cephalopods of danger. The ink from some cephalopods, like Heteroteuthis dispar, can glow in the dark because of a special light-producing substance.

Types of ink shapes

Cephalopods release ink in different shapes. There are six types: pseudomorphs, pseudomorph series, ink ropes, clouds or smokescreens, diffuse puffs, and mantle fills. These shapes help the cephalopod confuse predators by creating a messy, confusing cloud of ink in the water.

Inking behaviours

I was much interested, on several occasions, by watching the habits of an Octopus or cuttle-fish ... they darted tail first, with the rapidity of an arrow, from one side of the pool to the other, at the same instant discolouring the water with a dark chestnut-brown ink.

— Charles Darwin, The Voyage of the Beagle

Cephalopods, like octopuses and cuttlefish, use ink to escape from danger. When they feel threatened, they release a cloud of dark ink into the water. This ink acts like a smoke screen, making it hard for predators to see and helping the cephalopod escape quickly.

They also release smaller clouds of ink that look like their own bodies. These clouds can hold their shape and often trick predators into chasing them instead of the real cephalopod. Some cephalopods hide among long ropes of ink they release, blending in with nearby plants. They also protect their eggs by squirting ink at creatures that come close or by covering the eggs with ink to hide them from predators.

Use by humans

Cephalopod ink was once used to make ink for writing with pens and quills. The Greek name for cuttlefish, Sepia, comes from the brown colour of this ink.

Today, people use cephalopod ink mainly for cooking, especially in Japan and the Mediterranean. It adds colour and flavour to foods like pasta and sauces, such as a dish called calamares en su tinta. You can find it in markets and from food suppliers in places like Italy and Spain. The ink comes from the ink sacs of cephalopods, usually cuttlefish, and is prepared without any mucus.

Scientists are studying cephalopod ink to see if it can help fight certain cells, but more research is needed.