Sunday, 20 May 2012

Coelacanth - the 'fossil fish'

Last night was the 2012 edition of Museum Night, an international event when many museums are open to the public on a Saturday evening, generally until midnight.

Saint Denis' Natural History Museum (source)

We took the occasion to revisit Saint Denis' Natural History Museum, where there was a special exhibition about La Perouse, a famous French explorer whose two sailing vessels disappeared in 1788 in the South Pacific (they were later found to have been shipwrecked in the Solomon Islands).

In the one of the Museum's display cabinets is this impressive fish:

Coelacanth, Saint Denis' Natural History Museum

It's a West Indian Ocean coelacanth (Latimeria chalumnae), a fish that was known only through fossils and 'rediscovered' by scientists in 1938 off the coast of South Africa. Sole survivor of a very old group of fish thought to have become extinct over 70 million years ago, it was considered the 'missing link' between fish and tetrapods (vertebrate animals having four limbs). Its discovery by Captain Goosen off East London (South Africa) caused a sensation in the scientific world. It was preserved by local museum curator Marjorie Courtenay-Latimer, from whom it takes its Latin name.

Brass plate at Latimer's Landing, East London (source)

Found just before Christmas it was too big to fit in a bath, and no deep freeze could be found so it was wrapped in cloths soaked in formalin for four days before she could find a taxidermist could skin and preserve it - unfortunately the internal organs were lost in the process. South African university Professor JLB Smith identified and named the coelacanth, and initiated a search along East Africa for further specimens. It was 14 years before Captain Eric Hunt preserved a second specimen, from the Comoros. Local fishermen had long known of the fish's existence, but it was not targeted because it was poor eating.

Drawing of a coelacanth (source)

Coelacanths are primitive bony fish with lobed fins. Their scales have sharp prickly spines, and most of the skeleton is made of cartilage (like sharks). They can grow to be nearly 2 metres long and weigh up to 100kg. They have been found off Kenya (2), Tanzania (22), Mozambique (1), South Africa (24), Madagascar (4), and the Comoros (200+), and it's in this latter country that I saw this specimen in 2000 in Moroni's National Museum:

this coelacanth was caught in 1985

In the Comoros, where they are known as gombessa, most specimens have been caught off the islands of Grande Comore and Anjouan. Along with ylang-ylang cultivation (flowers used in perfume) the coelacanth is one of the small island nation's few claims to fame.

ylang-ylang in my garden

Individual coelacanths can be identified by the distinctive pattern of white spots on the dark slate coloured body. They eat a range of fish, squid and octopuses which they probably swallow whole, as un unusual 'hinge' in the head allows the coelacanth to open its mouth very wide. They are ovoviparous, which means that after mating and internal fertilisation the large eggs (about the size of an orange - 9 cm  diametre)  are retained in the female, and live young pups are born. (A single coelacanth caught in Mozambique contained 26 near-term pups each about 32 cm long).

Coelacanth anatomy (source)

About 120 species of coelacanth are known from fossils. In 1997 a separate  species, Latimeria menadoensis, was discovered to live off the coast Indonesia. In the western Indian Ocean they live at depths of 54-700 metres, and in 1998 the total population of the West Indian Ocean coelacanth was estimated to have been 500 or fewer; they are consequently considered critically endangered.

A few facts about the Comoros Islands:

photograph by French diver Laurent Ballesta

Related post:

Further reading:

Suggested books:

Dubious humour?

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