Wednesday, 5 December 2012

Elephantfish (Callorhinchus milii)


  The elephant shark, Callorhinchus milii, is a cartilaginous fish (Chondrichthyes). The strange looking Elephantfish has a hoe-shaped structure on the snout. 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.

  

Genome Project on Elephant Shark has launched to sequence the whole genome of the elephant shark. The elephant shark has three cone pigments for color vision (like humans). The elephant shark has a dorsal fin with a very sharp spine. The spine has been reputed to be venomous but no serious injuries have yet been reported. 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).
   Its most distinctive feature is a plough-shaped nose that is used to search for food on the seabed. The end of the flexible snout is covered in sensory pores that detect movement and weak electrical currents. Behind and close to the snout is a small mouth with crushing plates. The eyes are large and set high on the head, while the face of this chimaera is traced with a map of sensory mucus-filled canals. The single gill opening is immediately in front of each large sculptured pectoral fin. It is the pectoral fins that supply the animal’s primary means of locomotion.


Annual Migrations and Defence:

Males and females migrate from 200 m depths offshore to enter shallow coastal bays in spring and summer to breed. Here, females drop their golden-colored egg cases which hatch eight months later. Besides being well camouflaged, Elephant Fish defend themselves with a long serrated spine that is just in front of their first large dorsal fin. Elephant Fish often have green eyes, like the other chimaera species and deep-water sharks. When they are caught and hauled to the surface they have yet to react to the surface light and are still a startling metallic green. The body is silvery white, and sometimes has darker markings behind the eyes and on the fins.

Alternative Names:
Elephant Shark, Ghost Shark, Ghostshark, Plownose Chimaera, Reperepe, Silver Fish, White Fillets, Whitefish. 
    
Size range:
It grows to 1.2m in length.

Distribution:
The Elephantfish occurs off southern Australia and New Zealand.

Habitat:
It lives to depths of at least 200 and 500 meters deep on the continental shelf.

Other behaviors and adaptations:
The Elephantfish has a skeleton made of cartilage. Sharks and rays also have cartilaginous skeletons.
All three groups of fishes are classified in the class Chondrichthyes.

Life cycle:
In spring, females migrate into coastal bays and estuaries to lay their egg cases in sand and muddy substrates. The distinctively-shaped egg cases are sometimes found washed ashore after storms. They are up to 25 cm long, 10 cm wide, and take up to eight months to hatch.

Economic/social impacts:
It is caught commercially in New Zealand and Southern Australia.
                         
Classification:
Species:milii
Genus:Callorhinchus
Family:Callorhinchidae
Order:Chimaeriformes
Class:Chondrichthyes
Subphylum:Vertebrata
Phylum:Chordata
Kingdom:Animalia



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