Cuttlefish (Sepiida,) despite their name, are not fish at all, but molluscs. Cuttlefish belong to the class Cephalopoda, the same family as squid, octopus and nautilus. Cuttlefish are found in large numbers throughout the world’s oceans, from the warm tropical shallows, to the cold depths of the deep. Cuttlefish share the same characteristics as their relatives; squid, octopus and nautiluses, i.e. they have a large elongated body, with tentacles surrounding their mouth.
Cuttlefish are amazing and unique creatures. Most people have only heard of Cuttlefish being the piece of cuttlebone in a bird cage. However, the Cuttlefish is much more than a source of calcium for caged birds and hopefully after learning more about them, you will come to love and admire them as much as we do at Scubafish.
Interesting facts about Cuttlefish
There are 120 known species of Cuttlefish around the world, which vary in size, from 15 cm to the Australian Giant Cuttlefish, which is half a metre in length, excluding it’s tentacles.
Cuttlefish are considered to have the highest intelligence of any invertebrate. Cuttlefish have the most highly developed eyes of any animal and have the most acute polarization vision yet found in any animal. Polarization is an aspect of light that can provide animals with information about the world around them. Cuttlefish are colourblind and see aspects of light (including polarized light), that are invisible to humans, giving them a covert communication channel. They can actually see information in the angle of intense polarized light, that we can barely comprehend. The eyes of the Cuttlefish are fully developed before birth and start observing their surroundings while still in their transparent egg. They are likely to hunt the prey they saw before hatching.
Cuttlefish are masters of disguise and will quickly and constantly change the colour and texture of their skin, to blend into their surroundings. They change colour using a series of special skin cells; chromatophores, iridophores and leucophores, which reflect light in a variety of colours. They are able to reflect colours, imitate colours and merge completely with the sea bed, thus appearing invisible. The most spectacular colour displays occur when the Cuttlefish is stalking it’s prey, courting, fighting or warding off potential predators. They have the ability to flash colors or flicker displays across their bodies.
The Cuttlefish has an internal structure called the cuttlebone, which provides them with perfect buoyancy. They regulate their buoyancy by filling or emptying tiny compartments in their cuttlebone with fluid and gas, this helps them maintain neutral buoyancy. This also enables them to hover above the sea bed, because although they have a sophisticated propulsion system, their large cuttlebone does not allow them to be overly active. Cuttlefish use water-powered jet propulsion which involves drawing water into a compression chamber, which they expel from their mantle cavity (the funnel under their head.) They can change direction by swivelling the nozzle of this funnel and they can control their speed by narrowing the funnel.
Submarines are known to have adopted the Cuttlefish’s buoyancy techniques.
During the mating season, male Cuttlefish challenge one another for dominance and for the best den. During this challenge, no direct contact is made between the males. They threaten each other, until one of them backs down and swims away. They change their body colouring in order to successfully attract a female. They mate with the females by grabbing them with their tentacles, turning the female so that they are face-to-face, then using a specially modified tentacle (one of its eight tentacles), which inserts sperm sacs into an opening near the female’s mouth. The male guards the female until she lays her eggs, a few hours later. Some male Cuttlefish have even been known to make themselves look like a female Cuttlefish, in order to trick the dominant males and steal their mates. The female Cuttlefish lays around 200 small eggs and then sadly, dies soon afterwards.
The life span off a Cuttlefish is less than two years. Most Cuttlefish die shortly after a single spawning.
In common with other members of the Cephalopod family, Cuttlefish have an ink sack, which enables them to shoot out jets of ink to confuse predators, allowing them time to escape. Their ink was originally used by artists to create sepia. Nowadays this has been replaced with artificial sepia.
Cuttlefish do not have a tail, they have a fin which runs all the way around their body. They use this fin to control their movement in the same manner as a squid.
Cuttlefish have three separate hearts; one for both sets of gills and one for the rest of their body.
Cuttlefish blood looks blue-green, because it uses the pigment hemocyanin to carry oxygen, unlike our blood which uses the red pigment hemoglobin.
Cuttlefish are carnivores. They eat small mollusks, shrimps, crabs, fish, octopus and even other Cuttlefish, (they have been known to indulge in cannibalism!) They use their ability to change colour and texture to camouflage themselves. They catch their prey with the sucker pads on the end of their long tentacles and bring the prey into their sharp ‘beak-like’ jaws.
Due to their relatively small size, Cuttlefish have numerous predators; large fish, dolphins, sharks, seals, seabirds and even other Cuttlefish (sometimes of the same species.) They are also hunted by humans. According to The World Conservation Union (IUCN,) Cuttlefish are a threatened species.
Techniques and ideas when photographing Cuttlefish
- Cuttlefish make for a very photogenic, especially if you find them out hunting or mating
- Don’t crowd your subject, approach them slowly and don’t scare or startle them
- Never surround your subject, don’t chase after them and don’t ever touch them
- If you see them free swimming, get a sense of the general direction in which they are going and position yourself
- Carefully compose the image, the photograph should be sharply in focus
- If only one thing is in focus, it must be the eyes. Make the eye or eyes the focal point of the photograph, by doing this, people will be drawn to the image
- Macro shots: A close-up shot works really well, focusing on their unusual eyes. If you ever come across a Cuttlefish egg sac, this makes for an amazing shot, as the egg sac is transparent and the embryo is clearly visible
- A close-up portrait shot, with an external strobe and a plain background, preferably a black background makes for a really good photograph
- Be careful when positioning yourself, make sure not to disturb the seabed, as this can frighten other sea creatures and also cause a cloud of backscatter, making it impossible to take your photograph
- Using strobes or a camera’s internal flash, can help to create shadows and bring out textures, adding contrast to your photograph
- When you approach a Cuttlefish, it is likely it will notice your presence and start to display it’s warning signs; flashing colours, changing textures and raising it’s tentacles. When it’s displaying, use your camera’s continuous drive mode to fire off a few frames per second. Each image will likely come out very differently, as the cuttlefish rapidly changes it’s colours and positioning. Note that this is harder to achieve when using fiber optics to connect your strobes, as you must wait for your camera’s internal flash to recycle, which can take a few seconds.