Australian ghost shark
Encyclopedia
The elephant shark, 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 of the elephant shark include: Australian ghost shark, Makorepe, whitefish, plownose chimaeras or elephant fish. The latter is best avoided as it may be confused with elephantfishes (family Mormyridae
) which are freshwater teleost fishes from tropical Africa and the Nile.
It is found off southern Australia
, and south of East Cape
and Kaipara Harbour
in New Zealand
, at depths of 200 meters to 500 meters. Their length is between 60 and 120 centimeters. Males of this species mature at about 65 centimeters. During spring, adults migrate inshore to estuaries and bays where mating takes place and the females lay their eggs on sandy or muddy substrates. The eggs are contained in large yellowish capsules. The gestation
period is six to eight months. Elephant sharks are exploited commercially, particularly during spring and summer when they migrate into shallow coastal waters. The white flesh fillets of elephant shark are very popular with ‘fish-and-chips’ restaurants in New Zealand
and Australia
.
Recently, the elephant shark was proposed as a model cartilaginous fish genome
because of its relatively small genome size. The genome of the elephant shark is estimated to be 910 Mb long (Mb = megabases = 1 million basepairs) which is the smallest among all the cartilaginous fishes and one-third the size of the human genome
(3000 Mb). Because cartilaginous fishes are the oldest living group of jawed vertebrate
s, the elephant shark genome will serve as a useful reference genome for understanding the origin and evolution
of vertebrate
genomes including our own, which shared a common ancestor with elephant shark about 450 million years ago. Interestingly, studies so far have shown that the sequence and the gene order ("synteny”) are more similar between human and elephant shark genomes than between human and teleost fish genomes (fugu
and zebrafish) even though humans are more closely related to teleost fishes than to the elephant shark. Recently, an Elephant Shark Genome Project has been launched to sequence the whole genome of the elephant shark.
The elephant shark has three cone pigments for color vision (like H. sapiens).
The typical elephant has also a dorsal fin which alsos hosts a very sharp spine. This has been reputed to be venomous but no such serious injuries have yet been reported.***
Chondrichthyes
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
) belonging to the subclass Holocephali
Holocephali
The subclass Holocephali is a taxon of cartilaginous fish, of which the order Chimaeriformes is the only surviving group.Holocephali has an extensive fossil record that starts during the Devonian period. However, most fossils are teeth, and the body forms of numerous species are not known, or, at...
(chimaera
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...
). Sharks, rays and skates are the other members of the cartilaginous fish group and are grouped under the subclass Elasmobranchii
Elasmobranchii
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, that includes the sharks and the rays and skates .-Evolution:...
. Alternative names of the elephant shark include: Australian ghost shark, Makorepe, whitefish, plownose chimaeras or elephant fish. The latter is best avoided as it may be confused with elephantfishes (family Mormyridae
Mormyridae
The family Mormyridae, sometimes called "elephantfish" , are freshwater fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order with around 200 species. Members of the family are popular, if challenging, aquarium species...
) which are freshwater teleost fishes from tropical Africa and the Nile.
It is found off southern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, and south of East Cape
East Cape
East Cape is the easternmost point of the main islands of New Zealand. It is located to the north of Gisborne in the northeast of the North Island....
and Kaipara Harbour
Kaipara Harbour
Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Rodney District...
in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, at depths of 200 meters to 500 meters. Their length is between 60 and 120 centimeters. Males of this species mature at about 65 centimeters. During spring, adults migrate inshore to estuaries and bays where mating takes place and the females lay their eggs on sandy or muddy substrates. The eggs are contained in large yellowish capsules. The gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
period is six to eight months. Elephant sharks are exploited commercially, particularly during spring and summer when they migrate into shallow coastal waters. The white flesh fillets of elephant shark are very popular with ‘fish-and-chips’ restaurants in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Recently, the elephant shark was proposed as a model cartilaginous fish genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
because of its relatively small genome size. The genome of the elephant shark is estimated to be 910 Mb long (Mb = megabases = 1 million basepairs) which is the smallest among all the cartilaginous fishes and one-third the size of the human genome
Human genome
The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...
(3000 Mb). Because cartilaginous fishes are the oldest living group of jawed vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, the elephant shark genome will serve as a useful reference genome for understanding the origin and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
genomes including our own, which shared a common ancestor with elephant shark about 450 million years ago. Interestingly, studies so far have shown that the sequence and the gene order ("synteny”) are more similar between human and elephant shark genomes than between human and teleost fish genomes (fugu
Fugu
is the Japanese word for pufferfish and the dish prepared from it, normally species of genus Takifugu, Lagocephalus, or Sphoeroides, or porcupinefish of the genus Diodon. Fugu can be lethally poisonous due to its tetrodotoxin; therefore, it must be carefully prepared to remove toxic parts and to...
and zebrafish) even though humans are more closely related to teleost fishes than to the elephant shark. Recently, an Elephant Shark Genome Project has been launched to sequence the whole genome of the elephant shark.
The elephant shark has three cone pigments for color vision (like H. sapiens).
The typical elephant has also a dorsal fin which alsos hosts a very sharp spine. This has been reputed to be venomous but no such serious injuries have yet been reported.***