Abstract

Cuttlefish are among the most fascinating molluscs in the ocean. This paper provides background information about cuttlefish, their scientific designations, and anatomy. It then proceeds to explore numerous special qualities related to cuttlefish including camouflage, exceptional intelligence, acute vision, an enhanced hearing system, and unique movement abilities. In addition, this paper outlines best practices for maintaining cuttlefish as domestic pets and considers future evolutionary adaptations of this remarkable species. 

Background Information About Cuttlefish

Cuttlefish are marine mollusks that belong to the kingdom called Animalia. They are carnivorous cephalopods in the phylum mollusca. Cuttlefish have multiple genuses and are in the order sepiida with 6 families and over 120 different species. Their length ranges from 5.9 to 20 inches (15-50 centimeters) and they can weigh from 6.6 to 23 pounds (3-10 kilograms). These cephalopods live solitary lives eating crab fish and shrimp for 1-2 years before their demise. The average litter size of these animals is 200 (Britannica). As long as their habitats remain undisturbed by human activity, cuttlefish will likely continue to survive. 

Although their relatives are clams and snails, cuttlefish have many unique characteristics that help them thrive. For example, they possess three hearts. Two of these hearts are used to pump its single, versatile blood cell called hemoglobin to its gills. Meanwhile, their third heart pumps hemoglobin to their other organs. The majority of their 500-meter neurons are located in their mantle cavity, which is a central feature of molluscan biology (Lee et al. 39). This cavity is formed by the mantle skirt, a double fold of mantle which encloses a water space. Along the mantle are the fins which they use to move around. Underneath the cuttlefish is the belly which is paler than its upper parts. In front of the belly is the funnel, which can also be referred to as the siphon. Above the funnel is the head which has large eyes with W-shaped pupils. Cuttlefish also possess six arms and two tentacles that are used to catch prey and bring them to their beak. These arms not only have the sense of touch, but also that of taste and smell (Van Giesen 595).

Camouflage: Chameleons of the Sea

Cuttlefish are often known as the “chameleons of the sea” due to their excellent color-changing abilities (Deravi et al.). Their skin layer is a single cell in depth and there are different ways through which their camouflage works. Their eyes can send visual cues directly to their brain. As soon as the information reaches their brain, it tells the skin cells what to do (NOVA). One way that this process occurs relates to the multiple skin layers of the cuttlefish. The top layer is where they derive their colors. There are also red, yellow, and brown colored layers (NOVA). In addition, cuttlefish camouflage works through pigments. On the cuttlefish’s skin, there are small pigment sacks with muscles attached to them. The muscles can stretch their skin and then change its color (NOVA). They can also change the texture of their skin. The way this works is by the skin containing bands of circular muscle which, as they contract, push fluid up. These can be seen as little spikes, bumps, or flat blades. This can help with camouflage when the cuttlefish becomes texturally as well as chromatically similar to objects in its environment such as kelp or rocks (Hansford). 

There are many reasons why cuttlefish use camouflage. These reasons include evading predators, reproduction, and capturing prey. Cuttlefish are able to rapidly change the color of their skin to match their surroundings and create chromatically complex patterns (Stuart-Fox and Moussalli). They have the ability to assess their surroundings and match the color, contrast, and texture of the substrate even in nearly total darkness (Hansford). Depending on the species, the skin of cuttlefish responds to substrate changes in different ways. The Sepia Officinalis changes color to match the substrate by disruptive patterning, whereas S. Pharaonis matches the substrate by blending in. Although camouflage is achieved in different ways, and with an absence of color vision, both species change their skin colors to match their surrounding substrate. Cuttlefish adapt their own camouflage pattern in ways that are specific for a particular habitat. Cuttlefish could settle in the sand and appear one way, with another animal a few feet away in a different microhabitat, settled in algae for example, and will be camouflaged differently. On the other hand, flamboyant cuttlefish, a 2-inch species of cuttlefish that walk instead of swim, will flash their colors to warn predators that they are poisonous.

Another use for cuttlefish skin-changing abilities is hunting. The preferred diet of cuttlefish is crabs and fish. The broadclub cuttlefish use their skin to hypnotize prey by rapidly changing their color. Meanwhile, the giant cuttlefish use their skin as a way to ambush their prey by shooting two long tentacles and using their eight sucker pad covered arms to prevent them from escaping while they inject venom into their prey (Cousteau and Diolé). 

An additional way that cuttlefish use camouflage relates to reproduction. Certain species of male cuttlefish are known as “cross-dressers.” This is because they use their camouflage abilities to disguise themselves as females. “Changing their body color, and even pretending to be holding an egg sack, disguised males are able to swim past the larger guard male and mate with the female” (Hanlon et al.). This approach to reproduction is highly effective. In fact, female cuttlefish typically reject 70 percent of all mating approaches by males in general, but they only reject 30% of the cross-dressers (NOVA). In addition, the sperm received from cross-dressing males is given priority by females. Female cuttlefish can choose which sperm to use because it is kept in a pouch under their arms. They often select the sperm from cross-dressing cuttlefish (NOVA). Scientists hypothesize that this is the species’ way of prioritizing intelligence in future generations of cuttlefish. Camouflage also assists cuttlefish that try to win mates through fighting. When two cuttlefish are fighting over a mate, the one with the more terrifying color scheme tends to win. Interestingly, the one that usually wins is black and white (NOVA). 

Exceptional Intelligence 

The brain of a cuttlefish is wrapped around its esophagus and is the hub of its intelligence. Researchers believe that cuttlefish can be as intelligent as some birds and mammals (NOVA). They have large brain-to-body ratios, just as humans do. Their brain-to-body ratios may be even larger than those of octopi. Cuttlefish may not immediately know the difference between a toy fish and a real one but, with just one interaction, they can learn the difference (NOVA). Like a bird, they cannot see glass barriers; however, after hitting such barriers only a few times, they will realize that something is in front of them and stop hitting it. This suggests that they possess adaptive learning skills. Cuttlefish may also be capable of basic math skills. For example, they can determine whether certain quantities are greater or less than others. During one experiment, cuttlefish were shown two groups of shrimp. One of these groups had a larger amount of shrimp than the other. Interestingly, cuttlefish would always pick the side with more shrimp – even after the researchers spread the shrimp apart in each group. This shows that the cuttlefish did not choose by density but by quantity. 

Researchers placed individual cuttlefish (one at a time) into a bucket. The bucket had two openings. One opening was real and the other was fake because it had a glass barrier in front of it. The experiment was intended to teach the cuttlefish that, if they see a brick, they need to use the solid yellow door in order to escape. In addition, if they see a piece of seaweed, they have to use the black and yellow door to escape (NOVA). The fact that cuttlefish were able to succeed in this experiment demonstrates that they are capable of conditional discrimination learning.

Cuttlefish can also use their intelligence to exert self-control. This was demonstrated by an experiment that consisted of offering cuttlefish two food options: a headless dead shrimp and a living full-shelled one. Cuttlefish also associated different shape symbols with different types of food accessibility. “Our results demonstrate that cuttlefish can tolerate delays to obtain food of higher quality comparable to that of some large-brained vertebrates” (Schnell).  

Acute Vision

The eyes of cuttlefish are very large, especially when compared to the size of their bodies. This attribute can enable them to see well in conditions with low lighting. Cuttlefish move their extremely large eye lenses by reshaping their entire eyes. This “...may increase image magnification upon the retina, while the distinct ‘W’-shaped pupil helps control the intensity of light entering the eye” (Mäthger et al.). In addition to the largeness of their eyes, cuttlefish can use their eyes to judge distances in a similar way to humans. The process that they use to achieve this goal is called stereopsis (Guardian News). Stereopsis allows them “...to discern depth/distance because their brain calculates the input from both eyes” (Feord et al.). In addition to stereopsis, a distinguishing factor that enhances cuttlefish vision is that they can actually see whatever is behind them (Muller). Moreover, their retinas contain two different sensor cells. One of these cells allows them to see forward, and the other allows them to see backward. This ability gives them advantages such as being able to see predators that are stalking them before they can attack. 

Hearing Processes

Cuttlefish can detect sounds in the form of pressure waves using lateral epidermal lines and they can also hear low frequencies such as ultrasounds (Packard). The lines consist of thousands of hair cells that seem to be especially sensitive to sounds ranging from 75 to 100 Hertz (PBS.org). The ears of cuttlefish are known as statocysts. The statocysts change colors according to sound stimuli and cuttlefish stress levels. Statocysts are buried in cuttlefish heads and tuned to low-pitched sounds. This allows the animals to sense vibrations from a potential attack even in murky underwater conditions (Knight). When cuttlefish sense vibrations from a predator, they turn to flee in the opposite direction from the initial stimuli that they “heard.”

Unique Movement

Cuttlefish propel themselves with fins and water. They have a fin that lines the outside of their bodies. This fin looks like a skirt. When quick movement is needed, they can expel water and move by jet-propulsion. They have a multifunctional mantle cavity which holds 500 of their neurons. Cuttlefish suck water into the cavity and use their mantle muscles to push it out with a great deal of force in the opposite direction. In addition, this process brings water into the gills which filter oxygen into their bloodstream (PBS.org). Essentially, cuttlefish move by breathing. Cuttlefish can also use this technique to control their density and buoyancy. In addition, some types of cuttlefish, such as the two-inch Flamboyant cuttlefish, walk because they cannot float for very long due to having short buttlebones. 

How To Keep Cuttlefish As Pets

There are many practices that must be used to ensure that cuttlefish are properly maintained as pets. First, it is important to recognize that they primarily care about food, sex, and keeping their territory. As mentioned, cuttlefish do not need toys or other enrichment items to keep them occupied. As long as cuttlefish are kept in an environment stocked with food and other cuttlefish, they do not require much else. 

When considering the different types of rocks that can be added to an aquarium with cuttlefish, it is critical to avoid copper, zin, cadmium, and chromium. Cuttlefish are poisoned by these items so they cannot be put into aquariums. Furthermore, nitrates over 50 mgl should also be avoided because they can stunt cuttlefish growth and cause acute mortality. Moreover, cuttlefish can also be threatened by microbes such as Vibrio and Pseudomonas. Therefore, constant monitoring of water for these species is important. Cuttlefish are also sensitive to salinity and aquariums should consist of two parts of sodium per thousand parts of water. 

To prevent these problems, people who care for cuttlefish should use an oversized system, a protein skimmer, carbon or Granular Ferric Oxide reactor, and an auto top off (a device that controls the flow of water from a reservoir to an aquarium). This oversized system is important because cuttlefish tend to create a significant amount of waste and can become poisoned by the nitrates in their feces. 

There are a number of tank specifications depending upon which type of cuttlefish is kept as a pet. If people have a Bandensis cuttlefish, then the size of the cuttlefish will be approximately four to five inches long. The minimum display size per pair is approximately 30 gallons. The temperature range is approximately 74 to 80 degrees Fahrenheit. It is also important to note that pristine water is required for the proper maintenance of this species. In terms of decor, vertical structures are best suited for Bandensis cuttlefish. Moreover, the bottom of the tank can consist of any type of sand spacing, and is not limited to open sand. For flow, areas of low flow are highly recommended as opposed to high flow. In addition, any form of lighting can be used to help the Bandensis cuttlefish feel secure in their new habitat. Another type of cuttlefish that can be kept as a pet is the Pajama squid. The Pajama squid is around 2-5 inches long and the maximum capacity of its tank must be 20 gallons. It must have a temperature range between 60-76 Fahrenheit and the water must be in pristine condition. The bottom of the tank must be open with clam shells as decorations with low levels of flow and medium lighting. A different species of cuttlefish that can be kept as a pet is the 7-10 inches long Officinalis cuttlefish which also possesses unique tank specifications. The tank’s maximum display size for this type of cuttlefish has to be 75 gallons at 55-65 degrees Fahrenheit in pristine water. There should be open sand and fake seagrass at the bottom of the tank. The tank can have any lighting and any level of water flow.

Concluding Thoughts

In general, cuttlefish are already highly skilled at securing food, defending territory, and reproduction. Animals tend to evolve when some change is required. Yet, in the case of cuttlefish, there are few areas of improvement that are needed because they are so highly advanced. One potential change to future generations of cuttlefish may be related to the fact that they die when they mate. Nevertheless, they offset this pitfall by laying hundreds of eggs. Overall, however, this paper has demonstrated that cuttlefish are an extraordinary species in a number of areas. For example, their unique camouflage abilities are noteworthy because they can change the texture of their skin. They can use their camouflage to hide and hunt. Moreover, cuttlefish are intelligent creatures because they can do basic math and they learn quickly. Cuttlefish are also colorblind but can still change the color of their skin. Furthermore, scientists thought cephalopods like cuttlefishs were deaf until recently when it was discovered that they can hear very low frequency sounds called ultrasounds. Lastly, cuttlefish can control their density and buoyancy using their cuttlebone which allows them to float. Both in the wild and as domestic pets, this wondrous species will continue to thrive for years to come. 

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