African butterflyfish hides genetic surprise

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A team of scientists have discovered that African butterflyfish, (Pantodon buchholzi) from the two wild populations may look the same, but genetically they differ more than Chimpanzees and humans.

The scientists, including the Natural History Museum's Sebastien Lavoue, found huge differences of up to 15% in the mitochondrial genome between fish from the Congo and Niger populations.

Typically mitochondrial genome differences between specimens of one species are between 2% and 3%. A difference of 15% is what you might expect to find within an entire family of fish species. It was particularly unexpected as there had been no reports of morphological variation since the species was first described to science in 1876.

Using the latest techniques to estimate when this genetic divergence bega,n the team discovered that the separation of the two groups had occurred over 57 million years ago, yet despite this huge span of time and major climatic changes to the fish's habitat, the physical features of the butterflyfish had remained unchanged.

This means the fish could be considered 'living fossils', a term used for species that have remained unchanged for millions of years. Other examples of this include coelacanths and lampreys.

Lavoue hopes to further study the fish to discover just why they have stayed the way they have for so long. The two populations are now so different genetically that they may no longer be able to breed with one another, which could mean they are now in fact two cryptic species. To ascertain this, further study of their differences behaviourally and genetically is required.

The African butterflyfish is a popular 'oddball' addition to many aquariums. In the wild it lives in the calm waters of rainforest rivers, creeks and swamps. Growing to around 15cm/6", it swims just below the surface where it feeds on insects, small invertebrates and fish.