Australian ghost shark

Elephant shark
Elephant Shark, Melbourne Aquarium
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Holocephali
Order:	Chimaeriformes
Family:	Callorhinchidae
Genus:	Callorhinchus
Species:	C. milii
Binomial name
Callorhinchus milii Bory de Saint-Vincent, 1823

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 vertebrates, 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.***

References

• Reardon et al. (2003). Callorhinchus milii. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
• "Callorhinchus milii". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=564644. Retrieved 19 March 2006. 
• Froese, Rainer, and Daniel Pauly, eds. (2006). "Callorhinchus milii" in FishBase. January 2006 version.
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Nelson JS Fishes of the world (Wiley, New York 2006)
• P. R. Last and J. D. Stevens Sharks and Rays of Australia (Intl Specialized Book Service Inc June 1991) ISBN 978-0643051430
• Venkatesh B, Kirkness EF, Loh YH, Halpern AL, Lee AP, et al. (2007) Survey Sequencing and Comparative Analysis of the blurb(Callorhinchus milii) Genome. PLoS Biol 5(4): e101 doi:10.1371/journal.pbio.0050101

blurbsequencing project http://esharkgenome.imcb.a-star.edu.sg/ at Institute of Molecular and Cell Biology (Singapore)

• • • [(Vladimir I. - 2011)]