|Australian ghostshark at the Melbourne Aquarium|
Bory de Saint-Vincent, 1823
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, whitefish, plownose chimaera, or elephant fish.
It is found off southern Australia, including Tasmania, and south of East Cape and Kaipara Harbour in New Zealand, at depths of 0 - 200 m. Their length is up to 120 cm. Males of this species mature at about 65 cm. From spring to autumn, adults migrate inshore to estuaries and bays and females lay their eggs on sandy or muddy substrates. The eggs are contained in large yellowish capsules. The egg partially opens enabling seawater to flow in to the egg capsules after a few months and juveniles emerge from the capsule after six to eight months as about 12 cm in length. In New Zealand, Australian ghostsharks are exploited commercially, particularly during spring and summer when they migrate into shallow coastal waters. In Australia, they are caught by southern shark gillnet fishery, particularly in Bass Strait and south-east Tasmania, though this fishery targets the gummy shark, Mustelus antarcticus, and will sometimes discard ghostsharks due to the considerably lower price they fetch at market. They are also a popular target of recreational fishers in Westernport Bay, Victoria and in the inshore waters of south-east Tasmania. Their white flesh fillets are very popular with ‘fish-and-chips’ restaurants in New Zealand, but less so in Australia.
In January 2014, Nature reported research into the elephant shark (Callorhinchus milii) genome  that showed these chimaeras lack a single gene family that regulates the process of turning cartilage into bone, and indicates a gene duplication event gave rise to the transformation in bony vertebrates. .
The Australian ghostshark was proposed as a model cartilaginous fish genome because of its relatively small genome size. Its genome is estimated to be 910 megabases long, 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 vertebrates, the Australian ghostshark genome will serve as a useful reference genome for understanding the origin and evolution of vertebrate genomes including humans, which shared a common ancestor with the Australian ghostshark about 450 million years ago. Interestingly, studies so far have shown the sequence and the gene order ("synteny") are more similar between human and elephant shark genomes than between human and teleost fish genomes (pufferfish and zebrafish), though humans are more closely related to teleost fishes than to the Australian ghostshark. The Elephant Shark Genome Project was been launched with the aim to sequence the whole genome of the elephant shark.
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