Cephalopod ink

Cephalopod ink is a dark or glowing liquid that most species of cephalopods release into the water 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 dark colour of the ink is because of a substance called melanin. Different kinds of 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 a group of gastropods called sea hares, also use a similar trick to defend themselves when they are attacked.

Properties and chemistry

Cephalopod ink is made up 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 works by confusing the fish both visually and with chemicals. Some fish, like moray eels, have strong senses to detect chemicals, and ink may irritate or confuse these senses. Studies also show that ink can warn other cephalopods of danger. The ink from some cephalopods, like Heteroteuthis dispar, can even glow in the dark because of a special light-producing substance.

Types of ink shapes

Cephalopods release ink in different shapes, which are grouped into 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 as a clever way to escape from danger. When they sense a threat, they can release a large cloud of dark ink into the water. This ink works like a smoke screen, making it hard for predators to see and giving the cephalopod a chance to quickly jet away.

Another trick they use is releasing smaller, shaped clouds of ink that look like their own bodies. These clouds can hold their shape for a while and often trick predators into chasing them instead of the real cephalopod. Some cephalopods even hide among long ropes of ink they release, blending in with the ocean plants around them. They also protect their eggs by squirting ink at creatures that come too close or by covering the eggs with a layer of ink to hide them from hungry predators.

Use by humans

Cephalopod ink has been used in the past 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 mainly use cephalopod ink 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 to understand this better.