Ghost sharks, also known as chimaeras, are mysterious and elusive creatures of the deep sea. Despite their name, they are not actually sharks but belong to a unique group of cartilaginous fish closely related to sharks and rays. With their spooky appearance, large eyes, and long snouts, ghost sharks have captured the fascination of scientists and divers alike. These deep-dwelling creatures, found at depths of up to 8,500 feet (2,600 meters), possess a unique sixth sense that, coupled with specialized anatomy, allows them to thrive in the dark, high-pressure environments they inhabit. This article delves into the dietary habits of these enigmatic fish, exploring what they eat and how they find their food in the depths of the ocean.
Ghost Shark: An Overview
Ghost sharks are part of a group of cartilaginous fish called chimaeras. They are related to sharks but genetically diverged from their shark relatives nearly 400 million years ago. They are often called spookfish, ratfishes, or rabbitfishes due to their oddly shaped heads, ghastly coloration, and eerie, large black eyes. At least 38 known species of ghost sharks occupy the world’s ocean, the newest of which was discovered in 2009 in the Gulf of California, called the Eastern Pacific Black Ghost Shark. The Australian ghostshark (Callorhinchus milii) is a cartilaginous fish (Chondrichthyes) belonging to the subclass Holocephali (chimaera). Sharks, rays and skates are the other members of the cartilaginous fish group and are grouped under the subclass Elasmobranchii. Alternative names include elephant shark, makorepe (in Māori), whitefish, plough-nose chimaera, or elephant fish.
Ghost sharks have long tapering bodies and incredibly large heads. Their skin ranges in color from black to pale blue to brownish grey and is quite smooth. They have large eyes, oversized nostrils, and large, visible teeth, which give them a rabbit-like appearance, though within their mouths are three tooth plates. On their snouts are small club-shaped structures, atop their bodies are two dorsal fins, on the side are two pectoral fins for movement, and a dorsal fin is at the end of their tail. Their large, high-set eyes give off a green-ish glow due to a reflective tissue in their eyes called the tapetum lucidum, which helps vertebrates see better in low-light conditions.
Habitat and Distribution
Ghost sharks are difficult to observe since they occupy the deep sea, but we know they occupy most of the world’s ocean except for Antarctic waters. While some Chimaeras inhabit coastal areas, many prefer the deep ocean, thriving at depths of over 8,200 feet (2,500 meters). They live at depths ranging from 200 meters to 2,600 meters and generally stay close to the seafloor. This habitat requires them to adapt to low-light, high-pressure environments. Ghost Sharks are particularly well-suited to deep-sea life, with large eyes that help absorb any available light and fins that allow them to cover large distances with minimal energy. Their snouts, which are highly sensitive to electric fields, help them locate prey in the sand, and a venomous spine near their dorsal fin offers defense against predators lurking above. The elephant fish are demersal fish, meaning they live near the sea bed. They dive very deep into the ocean, thriving at depths of 600 to 5,000 ft below the surface. This chimaera resides on continental shelves of cool temperate areas to depths to at least 656 feet (200 m). At present this species is considered native to the waters of southern Australia and New Zealand.
Hunting and Feeding Strategies
Ghost Sharks feed mainly on benthic prey, including small fish, crustaceans, and other invertebrates. Ghost sharks use sensory organs on the club-like projection on their snouts to find prey in the dark waters in which they live. Using these organs, they can sense movement and weak electrical fields. The protruding snout, packed with electroreceptors, allows Chimaeras to detect prey hidden in the sandy ocean floor, adding to their arsenal of unique adaptations for survival in an environment where food can be scarce. The projection located on the snout is used to search for prey buried in the sand. The end is covered in pores that sense movement and weak electrical fields. The ghost shark is easy to recognize due to the small club-like structure located on the snout. Their protruding snout is made to search for food prey in the sand, and is highly sensitive to electric fields and movement. Elephant fish can often detect the movements of other fish of their species via pores in their snout.
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Diet Composition
The diet of this fish is based on small, soft invertebrate animals that live on the ocean floor, like octopi, mollusks, shrimp, and shellfish. As bottom feeders, they will eat almost any invertebrate in their path, including small octopi, squid, worms, crustaceans, starfish, brittlestars, shrimp, sea cucumbers, and sea urchins. Their diet primarily consists of shellfish, mollusks, and worms that live on or under the seafloor. Ghost sharks are carnivorous fish that feed on deep-sea invertebrates such as small octopuses, jellyfish, and mollusks. The elephant fish is commonly feeding on mollusks or other invertebrates on the ocean floor of the South Pacific ocean.
Specialized Anatomy for Feeding
Ghost sharks have three pairs of hypermineralized tooth plates. Their specialized tooth plates are perfect for crushing hard-shelled organisms, making them effective hunters in the ocean’s depths. The anterior tooth plates of the upper jaw are sharp and blade-like while the anterior tooth plates of the lower jaw are flat used for crushing hard prey items. Their dental plates help them catch, crush, and swallow their prey. The teeth of the ghost shark continue to grow and are not shed and replaced as they are in sharks. The mouth is located just behind the snout.
Predators
Larger sharks are natural predators of ghost sharks. It is often preyed on by larger fish, such as sharks. The dorsal fin in the middle of their back has a long spine that they use to defend themselves. Ghost sharks have a long spine located just in front of the first dorsal fin and is used to defend themselves against potential predators.
Conservation Status and Threats
The IUCN lists various Chimaera species under different threat levels, with many classified as "Near Threatened" or "Vulnerable." The primary threat to Ghost Sharks is bycatch, as they are often unintentionally captured in deep-sea fishing gear. Ghost sharks are often bycatch, or caught unintentionally, in trawl fisheries. Ghost sharks are targeted by commercial fisheries off New Zealand.
Human Interaction and Research
While Ghost Sharks don’t interact directly with humans due to their deep-sea habitats, they hold significant scientific interest. Their slow-evolving genome offers insights into vertebrate evolution, as Chimaeras are one of the oldest living fish lineages on the planet. Ghost sharks have a long spine located just in front of the first dorsal fin and is used to defend themselves against potential predators. Despite their elusive nature, Ghost Sharks occasionally enter shallower waters, allowing divers to glimpse them. In recent years, researchers have focused on their adaptations to the deep-sea environment, exploring how characteristics like Deep-Sea Gigantism help them thrive. Since Ghost sharks are primarily deep sea dwellers, it is rare to have opportunities to dive with these creatures.
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The Australian Ghost Shark (Elephant Fish)
The elephant fish, also known as the Australian ghost shark, is a unique-looking fish with an elongated, protruding snout. It is commonly feeding on mollusks or other invertebrates on the ocean floor of the South Pacific ocean. Elephant fish are about 2-4 feet in length. That’s the average height of a 3-6-year-old toddler! Once fully mature, they weigh about 10-15 lbs, but larger fish can even get as heavy as 20lbs if they have a rich diet. These are some of the most recognizable fish due to their outward extended snout. They have two dorsal fins, one near their head and one in the middle of their back. Their eyes are high on their heads and are a yellow-green color. Elephant fish are solitary animals. They only pair up when breeding. They spend most of their time scouring the bottom of the ocean, feeding on the muddy and sandy seafloor. Elephant fish are carnivorous fish that feed on deep-sea invertebrates such as small octopuses, jellyfish, and mollusks. Elephant fish can often detect the movements of other fish of their species via pores in their snout.
Reproduction and Life Cycle
Ghost sharks are oviparous reproducers, which means they release fertilized egg cases into the water during the spring months. These fish usually mate in the spring and early summer (from October to January in the southern hemisphere). When mating, the males and females rise from the bottom of the sea to shallower waters. The males have claspers that allow them to transfer their sperm to the female. The female then goes to even shallower waters to lay the eggs. Their keratinous eggs are then released onto the sandy ocean floor. These egg cases are golden yellow in color and settle onto the ocean’s sandy or muddy floor depending on where in the ocean they are. At the beginning of the incubation period, the eggs are yellow in color, then they become brown, and they turn black right before they hatch. Incubation takes about 8 months, during which time the embryos feed on the yolk of their individual eggs. Before hatching, the egg cases appear black or brown. Elephant fish males usually mature at around 3 years of age. Once hatched, the baby elephant fish are around 2-6 inches in length, depending on the nutrition they receive during their incubation. Their babies are known as pups. The egg case of these pups has a horny edge on one end, the end they crawl out of when they hatch. They usually hatch between October and November. The pups will stay in shallow waters for the first few weeks before they swim deeper into the ocean. Elephant fish live an average of 10 years, but in some cases, they have been known to live as long as 15 years. Males reach maturity at 2-3 years of age, corresponding to 19.7 inches (50 cm) total length, while females mature at 4-6 years of age and 27.6 inches (70 cm) total length.
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