Weird fish of the week: Plough-nosed chimaera


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This week's weird fish candidate certainly fits the bill, especially when the order they belong to is the Chimaeriformes, which basically translates as "monster shaped"....

Callorhinchus milii, more commonly known as the Plough-nosed chimaera or Ghost shark, is certainly an odd looking creature, as are all the Chimaera species which are thought to be among the oldest groups of fish living today, with an ancestry going back over 400 million years.

The origin of Callorinchus millii's common name is as plain as the nose on its face – the tip of its rostrum is extended into an odd, twisted club-like structure. Ironically given the etymology of its order's name the family's name "Callorhinchus" comes from the Greek for "beautiful snout". This peculiar proboscis is covered with sensory pores with which the fish can detect the weak electrical fields and movement of potential prey buried in the seabed as it roots around for a meal which typically consists of shellfish and small crustaceans which are crushed up by the fish's tooth plates.

They are a cartilaginous fish, related to sharks and to some extent share a similar body shape but with some clear differences. They have enlarged pectoral fins which they flap in a wing-like manner for swimming similar to rays in preference to using their tails.

The first of their two dorsal fins is home to a large venomous spine that can be used defensively. The chimaera's body is smooth and scale-less with a beautiful silvery white metallic background colouration, punctuated by dark blotches.

Its large, green eyes point to its natural habitat which is typically at depths of over 200m off the temperate coasts of Australia and New Zealand in the South-west Pacific.

They do however come into shallow water to breed with females laying large, flattened, leathery eggs onto the sea bed. These eggs harden and darken in colour as the embryo matures. The young eventually hatch out after about eight months of living on their yolk sack at around 15cm/6" long.

Adult Plough-nosed chimaeras can live to 15 years and grow to around 125cm/4'.

Despite being a popular food fish in fish and chip restaurants in Australia and New Zealand, their population remains stable and the species is not considered to be at risk.

Callorhinchus milii has recently been the subject of considerable scientific research with its genome being mapped. It has the smallest genome among known cartilaginous fish at about one third the size of the human genome. It is hoped this work will help further understanding of the evolution of vertebrates, as both humans and the chimaera share a common ancestor from 450 million years ago.