Giant Cuttlefish What is a Cuttlefish?
Giant cuttlefish can grow up to 1m in length (including outstretched tentacles) and weigh as much as 10kg. They are intelligent animals that can put on spectacular colour and light displays and alter the shape and texture of their bodies to imitate their environment.
Giant cuttlefish are cephalopods and are related to squid and octopuses. They are not fish, as their name may suggest.
The scientific name for the giant cuttlefish is Sepia apama.
The giant cuttlefish is the largest cuttlefish of them all. It can grow a mantle (body) of 5cm with an additional 5cm when the length of its tentacles is included, giving it a total length of up to one meter. It can weigh as much as 10 kilos. Cuttlefish are believed to be very intelligent. They have one of the largest brain-to-body mass ratios of any invertebrate.
The giant cuttlefish are masters of disguise and an expert at camouflage and colour change. It can quickly change its body's colour, pattern, and texture using millions of tiny skin cells known as chromatophores. Sometimes, playing a magician, it can even make shapes with its tentacles to mesmerise its prey or to better blend into the background.
The giant cuttlefish has eight arms and two tentacles. These arms and tentacles do not have bones. Instead, they are built from an intricate tapestry of coiled muscle fibres. The cuttlefish's two tentacles are specially adapted to extend at lightning speed to snatch prey. While its eight arms are specialised for grasping its prey once the cuttlefish has captured it with its two elongated tentacles. The cuttlefish also uses its arms for defensive display. Here the cuttlefish sucks water into its mantle cavity and spreads its arms wide to appear larger to its potential opponent.
The giant cuttlefish has relatively large outward-facing eyes with "W" shaped pupils that give them 360-degree vision. While it is colour-blind, it has excellent low-light visibility. And has one of the most sophisticated eyes of any animal.
The cuttlefish has a pair of undulating skirt-like fins that span the length of its mantel and help it swim and manoeuvre. If rapid movement is required, it propels itself backwards by shooting a jet of water from its gut.
The cuttlefish has a single internal bone-like structure called a cuttlebone, hence its name—cuttle-fish. This hollow and porous inner shell supports the fleshy parts of its body and gives it buoyancy. This cuttlebone acts like a swim bladder in fish and allows the animal to control the depth at which it lives. (White cuttlefish bones from dead cuttlefish are often washed up on beaches.)
The giant cuttlefish has three hearts, with two pumping blood to its large gills and one circulating the oxygenated blood to the rest of its body. Its blood is blue-green in colour because it contains a copper-containing protein called haemocyanin to transport oxygen through its body. (Mammals use the iron-rich protein haemoglobin for the same purpose).
The giant cuttlefish has a lifespan of two to four years and is mainly active during the day.
The giant cuttlefish lives in rocky coral reefs, seagrass beds, and sand and mud seafloors at depths of up to 100 meters. It is found along the south-eastern coast of Australia, from Moreton Bay in Queensland to the Ningaloo Reef of Western Australia. It does not swim at depths of more than 100 meters, as the water pressure at these depths would cause its cuttlebone to implode (collapse), causing its death.
The giant cuttlefish eats fish, crabs, molluscs, shellfish, crustaceans and even other cuttlefish. It is an active and aggressive hunter that uses its colour-changing skills and tentacles to mesmerise its prey before pouncing on it. It may also camouflage itself and wait until an unsuspecting prey swims by to quickly grab it. The giant cuttlefish uses its parrot-like beak at the base of its arms to bite and subdue its prey. It also uses this sharp beak to defend itself from predators and other cuttlefish.
Giant cuttlefish spawn between April and September. During this breeding season thousands of cuttlefish come together to spawn. During this time, male cuttlefish put on extravagant mating displays. They alter the colour and texture of their skin, flare their arms and produce pulsating zebra stripes along the sides of the body to attract females and intimidate potential rivals. Smaller males sometimes mimic the colouration and behaviour of females and sneak up to females to mate with them without the larger aggressive males being aware of their deception.
Mating takes place head-to-head. The male transfers spermatophores, or small packages of sperm, to a particular area of the female where fertilisation takes place.
Shortly after fertilisation, the female lays 100 and 300 lemon-shaped, leathery white eggs in sub-tidal crevices where the water temperature is around 12°C. Unlike many other cephalopods, female cuttlefish do not guard their eggs. Instead, the female abandons her egg and leaves them to hatch. The young hatch in 3-5 months.
Cuttlefish Predators and Threats
Natural predators of cuttlefish include dolphins, sharks, large fish, seals, sea birds, and other cuttlefish. When threatened, a cuttlefish may squirt a jet of black ink to confuse its predators while it makes a hasty getaway.
Conservation Status Is the Cuttlefish Endangered?
The number of giant cuttlefish has declined drastically over recent years. They are impacted by overfishing and habitat degradation. The Giant Cuttlefish is also threatened by increased salinity levels which reduce the success of eggs hatching.
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