Cuttlefish

What are cuttlefish?

Despite their name, cuttlefish are not fish but intelligent invertebrates related to the octopus, squid, and nautilus. These fascinating creatures can count, exert self-control, and have numerous wily tactics to evade predators, including creating their own body double from a cloud of ink. Despite being colorblind, cuttlefish also have highly sophisticated color-changing abilities.

The more than 120 different species of cuttlefish are usually solitary animals and can be found in oceans all around the world. While most live in shallow waters, some species can be found at depths of more than 3,000 feet.

Appearance and behavior

These cephalopods (which means “head foot”) have eight arms and two long tentacles attached directly to their head. The mantle—the area behind the eyes which contains the cuttlefish’s internal organs—is surrounded by a fringe-like fin that flaps in a rippling motion for maneuvering.

Cuttlefish control buoyancy using an internal shell called the cuttlebone. By adding different amounts of liquid or gas into tiny holes within this structure, these animals can change their buoyancy, making them float up or down. They can also move using jet propulsion: filling their body cavities with water then forcefully squirting it out to propel themselves backward.

These predators feed on fish, crabs, prawns, smaller cuttlefish, and shrimp, using extendable tentacles to grab prey which they immobilize with a toxic bite. The cuttlefish’s beak, located at the base of its arms, is sharp enough to break hard crab shells.

Intelligence

Cuttlefish have a large brain-to-body size ratio—among the biggest of all invertebrates—which makes them incredibly intelligent. They can count and can remember what, where, and when they last ate; a memory trait once believed to be unique to humans. Unlike many human toddlers, they can even pass the marshmallow test: A 2021 study found cuttlefish can will eat less food earlier if they know they will be rewarded with shrimp, their favorite treat, if they wait.

Masters of camouflage

Like other cephalopods, cuttlefish are masters of disguise. By controlling the 10 million color cells within their skin, they can quickly change color, pattern, and texture—sometimes completing the illusion by making shapes with their tentacles to better blend into the background.

These disguises help them deter or evade predators, mimic other species to catch prey, and communicate with other cuttlefish. They can even display two messages at once: At least one male cuttlefish has been spotted simultaneously wooing a female mate by flashing courtship colors on one flank while disguising itself as a female on the other flank to trick a male rival.

Vision

Although renowned for their color-changing ability, these "chameleons of the sea" are colorblind. They have distinctive W-shaped pupils, which allow them to see almost entirely behind them and may even be able to switch between forward-facing and peripheral vision.

Unlike humans, cuttlefish can detect differences in polarized light, which adds an extra dimension to their vision by allowing them to perceive the angle at which light is reflected when it bounces off a surface. In fact, they have more acute polarized vision than any other animal.

Evading predators

Preyed on by dolphins, sharks, large fish, sea lions, and even other cuttlefish, these soft-bodied mollusks have several self-defense tactics. Camouflage helps them merge into the background and they spend 95 percent of their time in hiding. Another defense mechanism involves squirting a cloud of ink as a distraction while the cuttlefish tries to escape, sometimes even mixing mucus with the ink to create a “pseudomorph” in the shape of their body as a decoy.

When hunted, cuttlefish adapt their response to the predator: striking, intimidating visual displays to discourage those that hunt by sight or simply swimming away from those that find prey through other senses. To avoid sharks, which detect the electrical currents emitted by prey, cuttlefish minimize these electric signals by freezing, covering their body with their arms, and slowing their breathing.

Mating behavior

During courtship, male cuttlefish put on a dazzling display to attract females—over whom rival males will fight viciously. Males will pass a packet of sperm to the female, who stores sperm from several males in her mouth cavity until she chooses which to use for fertilization. To maximize chances of reproductive success, males can shoot water into a female’s mouth to displace other males’ sperm packets before depositing theirs.

 When a female is ready, she finds a safe spot to lay and fertilize her eggs, which are called sea grapes because they are set in bunches and stained black by the mother’s ink. Cuttlefish die after reproduction, usually at around two years old.

Threats to survival

Most species of cuttlefish are not endangered. However, the International Union for the Conservation of Nature lists the giant Australian cuttlefish (Sepia apama) as near threatened and notes that the ocean acidification caused by increased carbon dioxide in the atmosphere is potentially a threat to all cuttlefish. Meanwhile, the common cuttlefish (Sepia officinalis) have been declared endangered along Britain’s south coast from overfishing.